diff -u b/core/modules/mysql/mysql.install b/core/modules/mysql/mysql.install
--- b/core/modules/mysql/mysql.install
+++ b/core/modules/mysql/mysql.install
@@ -31,8 +31,7 @@
         $query = 'SELECT @@SESSION.transaction_isolation';
       }
 
-      $tables_missing_key = [];
-      $missing_primary_key = FALSE;
+      $tables_missing_primary_key = [];
       $tables = $connection->schema()->findTables('%');
       $isolation_level = $connection->query($query)->fetchField();
       $severity_level = REQUIREMENT_INFO;
@@ -41,22 +40,21 @@
       foreach ($tables as $table) {
         $primary_key_column = Database::getConnection()->query("SHOW KEYS FROM {" . $table . "} WHERE Key_name = 'PRIMARY'")->fetchAllAssoc('Column_name');
         if (empty($primary_key_column)) {
-          $missing_primary_key = TRUE;
-          $tables_missing_key[] = $table;
+          $tables_missing_primary_key[] = $table;
         }
       }
 
-      $tables_missing_key_text = 'For this to work properly all tables should have a primary key. The following table(s) do no have a primary key: ' . implode(', ', $tables_missing_key);
+      $tables_missing_primary_key = 'For this to work properly all tables should have a primary key. The following table(s) do no have a primary key: ' . implode(', ', $tables_missing_primary_key);
 
-      if ($isolation_level == 'READ-COMMITTED' && $missing_primary_key) {
+      if ($isolation_level == 'READ-COMMITTED' && !empty($tables_missing_primary_key)) {
         $severity_level = REQUIREMENT_ERROR;
-        $description = 'This site is using the database transaction level "READ COMMITTED". ' . $tables_missing_key_text;
+        $description = 'This site is using the database transaction level "READ COMMITTED". ' . !empty($tables_missing_primary_key);
       }
       elseif ($isolation_level == 'REPEATABLE-READ') {
         $severity_level = REQUIREMENT_WARNING;
         $description = 'This site is using the database transaction level "REPEATABLE READ". The recommended database transaction level for Drupal is "READ COMMITTED".';
-        if ($missing_primary_key) {
-          $description .= ' ' . $tables_missing_key_text;
+        if ($tables_missing_primary_key) {
+          $description .= ' ' . $tables_missing_primary_key;
         }
       }
       elseif ($isolation_level == 'READ-UNCOMMITTED' || $isolation_level == 'SERIALIZED') {
diff -u b/core/modules/mysql/src/Driver/Database/mysql/Connection.php b/core/modules/mysql/src/Driver/Database/mysql/Connection.php
--- b/core/modules/mysql/src/Driver/Database/mysql/Connection.php
+++ b/core/modules/mysql/src/Driver/Database/mysql/Connection.php
@@ -205,11 +205,9 @@
     ];
     // Only set the transaction isolation level when the connection option has
     // been set to 'READ COMMITTED' or 'REPEATABLE READ'.
-    if (!empty($connection_options['isolation_level']) &&
-      in_array($connection_options['isolation_level'],
-        ['READ COMMITTED', 'REPEATABLE READ'], TRUE)) {
+    if (!empty($connection_options['isolation_level']) && in_array(strtoupper($connection_options['isolation_level']), ['READ COMMITTED', 'REPEATABLE READ'], TRUE)) {
       $connection_options['init_commands'] += [
-        'isolation_level' => 'SET SESSION TRANSACTION ISOLATION LEVEL ' . $connection_options['isolation_level'],
+        'isolation_level' => 'SET SESSION TRANSACTION ISOLATION LEVEL ' . strtoupper($connection_options['isolation_level']),
       ];
     }
 
reverted:
--- b/core/modules/mysql/tests/src/Functional/mysql/PrimaryKeyExistsTest.php
+++ /dev/null
@@ -1,68 +0,0 @@
-<?php
-
-namespace Drupal\Tests\mysql\Functional\mysql;
-
-use Drupal\Core\Database\Database;
-use Drupal\Tests\BrowserTestBase;
-
-/**
- * Tests isolation level warning when the config is set in settings.php.
- *
- * @group mysql
- */
-class PrimaryKeyExistsTest extends BrowserTestBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  protected static $modules = ['mysql'];
-
-  /**
-   * {@inheritdoc}
-   */
-  protected $defaultTheme = 'stark';
-
-  /**
-   * Test the isolation level warning message on status page.
-   */
-  public function testAllTablesOnPrimaryKey() {
-    $connection = Database::getConnection();
-
-    $admin_user = $this->drupalCreateUser([
-      'administer site configuration',
-      'access site reports',
-    ]);
-    $this->drupalLogin($admin_user);
-
-    // Check the message is not a warning.
-    $this->drupalGet('admin/reports/status');
-    $elements = $this->xpath('//details[@class="system-status-report__entry"]//div[contains(text(), :text)]', [
-      ':text' => 'To insure correct operation with READ-COMMITTED, ensure all tables have a primary key.',
-    ]);
-    $this->assertCount(1, $elements);
-    $this->assertStringNotContainsString('warning', $elements[0]->getParent()->getParent()->find('css', 'summary')->getAttribute('class'));
-
-    $connection->schema()->createTable('test_primary_key', [
-      'fields' => [
-        'id' => [
-          'type' => 'int',
-          'unsigned' => TRUE,
-          'not null' => TRUE,
-        ],
-      ],
-    ]);
-
-    $this->assertTrue($connection->schema()->tableExists('test_primary_key'));
-
-    // Check the message is not a warning.
-    $this->drupalGet('admin/reports/status');
-    $elements = $this->xpath('//details[@class="system-status-report__entry"]//div[contains(text(), :text)]', [
-      ':text' => 'To insure correct operation with READ-COMMITTED, ensure all tables have a primary key. The following table(s) do not contain a primary key: test_primary_key',
-    ]);
-    $this->assertCount(1, $elements);
-    // Ensure it is a warning.
-    $this->assertStringContainsString('warning', $elements[0]->getParent()->getParent()->find('css', 'summary')->getAttribute('class'));
-
-  }
-
-}
reverted:
--- b/core/phpstan-baseline.neon
+++ a/core/phpstan-baseline.neon
@@ -2955,6 +2955,11 @@
 			count: 12
 			path: tests/Drupal/KernelTests/Core/Cache/GenericCacheBackendUnitTestBase.php
 
+		-
+			message: "#^Variable \\$expected_driver might not be defined\\.$#"
+			count: 2
+			path: tests/Drupal/KernelTests/Core/Database/DriverSpecificKernelTestBase.php
+
 		-
 			message: "#^Relying on entity queries to check access by default is deprecated in drupal\\:9\\.2\\.0 and an error will be thrown from drupal\\:10\\.0\\.0\\. Call \\\\Drupal\\\\Core\\\\Entity\\\\Query\\\\QueryInterface\\:\\:accessCheck\\(\\) with TRUE or FALSE to specify whether access should be checked\\.$#"
 			count: 75
reverted:
--- b/core/tests/Drupal/FunctionalTests/Core/Database/DriverSpecificBrowserTestBase.php
+++ /dev/null
@@ -1,21 +0,0 @@
-<?php
-
-namespace Drupal\FunctionalTests\Core\Database;
-
-use Drupal\Tests\BrowserTestBase;
-use Drupal\Tests\DriverSpecificTrait;
-
-// cSpell:ignore mymodule mydriver
-
-/**
- * Base class for driver specific browser tests.
- *
- * Driver specific tests should be created in the
- * \Drupal\Tests\mymodule\Functional\mydriver namespace,
- * and their execution will only occur when the database
- * driver of the SUT is provided by 'mymodule' and named 'mydriver'.
- */
-abstract class DriverSpecificBrowserTestBase extends BrowserTestBase {
-  use DriverSpecificTrait;
-
-}
reverted:
--- b/core/tests/Drupal/KernelTests/Core/Database/DriverSpecificKernelTestBase.php
+++ a/core/tests/Drupal/KernelTests/Core/Database/DriverSpecificKernelTestBase.php
@@ -31,7 +31,6 @@
     // is not the one the test requires, skip before test database
     // initialization so to save cycles.
     $this->root = static::getDrupalRoot();
-    $expected_driver = '';
     $connectionInfo = $this->getDatabaseConnectionInfo();
     $test_class_parts = explode('\\', get_class($this));
     $expected_provider = $test_class_parts[2] ?? '';
reverted:
--- b/core/tests/Drupal/Tests/DriverSpecificTrait.php
+++ /dev/null
@@ -1,59 +0,0 @@
-<?php
-
-namespace Drupal\Tests;
-
-use Drupal\Core\Database\Connection;
-use Drupal\Core\Database\Database;
-
-/**
- * Provides a Traits Driver Specific.
- */
-trait DriverSpecificTrait {
-
-  /**
-   * The database connection for testing.
-   *
-   * @var \Drupal\Core\Database\Connection
-   */
-  protected Connection $connection;
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp(): void {
-    // Find the current SUT database driver from the connection info. If that
-    // is not the one the test requires, skip before test database
-    // initialization so to save cycles.
-    $this->root = static::getDrupalRoot();
-    $expected_driver = '';
-
-    if (method_exists($this, 'getDatabaseConnectionInfo')) {
-      $connectionInfo = $this->getDatabaseConnectionInfo();
-    }
-    else {
-      $connectionInfo = Database::getConnectionInfo();
-    }    $test_class_parts = explode('\\', get_class($this));
-    $expected_provider = $test_class_parts[2] ?? '';
-    for ($i = 3; $i < count($test_class_parts); $i++) {
-      if (in_array($test_class_parts[$i], ['Kernel', 'Functional'], TRUE)) {
-        $expected_driver = $test_class_parts[$i + 1] ?? '';
-        break;
-      }
-    }
-    if ($connectionInfo['default']['driver'] !== $expected_driver) {
-      $this->markTestSkipped("This test only runs for the database driver '$expected_driver'. Current database driver is '{$connectionInfo['default']['driver']}'.");
-    }
-
-    parent::setUp();
-    $this->connection = Database::getConnection();
-
-    // After database initialization, the database driver may be not provided
-    // by the expected module; skip test in that case.
-    $running_provider = $this->connection->getProvider();
-    $running_driver = $this->connection->driver();
-    if ($running_provider !== $expected_provider || $running_driver !== $expected_driver) {
-      $this->markTestSkipped("This test only runs for the database driver '$expected_driver' provided by the '$expected_provider' module. Connected database driver is '$running_driver' provided by '$running_provider'.");
-    }
-  }
-
-}