"Source database does not contain a recognizable Drupal version" error message

I was having same issue. Please check if you have any table prefix then you need to add in "ADVANCED OPTIONS" there is a option "Table name prefix" .

@f1mishutka, Thanks for reporting this issue.

I have tested this on 8.7.x and 9.1.x and am unable to reproduce the problem. I used a source database with a system schema of '6056'.

MariaDB [d6_dump]> SELECT schema_version FROM `system` where name='system';
+----------------+
| schema_version |
+----------------+
|           6056 |
+----------------+
1 row in set (0.000 sec)

Since I can' reproduce this issue on the Drupal version it was reported against or the latest version, I'm marking the issue "Closed (cannot reproduce)". If anyone can provide complete steps to reproduce the issue (starting from "Install Drupal core"), document those steps in the issue summary and set the issue status back to "Active".

Thanks!

Problem occurs again.
Migration from 7.84 to 8.9.20

Mysql is an mysql/mysql-server:8.0

Problem occurs with check of LegacyVersion its trying to access in the d7 database:
> SELECT schema_version FROM system where name='system';

Mysql Error: ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'system where name='system'

There are missing the backticks "`" around the tablename "system" because system is a reserved word in Mysql-8

Fix for migration was in web/core/lib/Drupal/Core/Database/Connection.php

# diff -Nur web/core/lib/Drupal/Core/Database/Connection.php web/core/lib/Drupal/Core/Database/Connection.php.new 
--- web/core/lib/Drupal/Core/Database/Connection.php	2022-01-01 21:14:23.406990150 +0000
+++ web/core/lib/Drupal/Core/Database/Connection.php.new	2021-12-30 23:15:52.316692460 +0000
@@ -313,9 +313,9 @@
     }
     // Then replace remaining tables with the default prefix.
     $this->prefixSearch[] = '{';
-    $this->prefixReplace[] = "" . $this->prefixes['default'];
+    $this->prefixReplace[] = "`" . $this->prefixes['default'];
     $this->prefixSearch[] = '}';
-    $this->prefixReplace[] = '';
+    $this->prefixReplace[] = '`';
 
     // Set up a map of prefixed => un-prefixed tables.
     foreach ($this->prefixes as $table_name => $prefix) {

Please verify on Drupal 9.