The website encountered an unexpected error

I think the thing to do is to use apply spaceless instead of spaceless and endapply instead of endspaceless.

Patch on request.

provided patch for the issue spaceless is deprecated in Twig 3.*.

The patch in #3 applies but it doesn't include all the cases. I added an additional patch that should be used in addition to the other patch.

Hi, I have tested this issue in Drupal 9.5.x and Drupal 10.1.x.

When i install this theme in Drupal 9.5.x it showing this error:-

The website encountered an unexpected error. Please try again later.

Drupal\Core\Config\PreExistingConfigException: Configuration objects (block.block.footer) provided by potent_allure already exist in active configuration in Drupal\Core\Config\PreExistingConfigException::create() (line 65 of core\lib\Drupal\Core\Config\PreExistingConfigException.php).
Drupal\Core\Config\ConfigInstaller->checkConfigurationToInstall('theme', 'potent_allure') (Line: 132)
Drupal\Core\ProxyClass\Config\ConfigInstaller->checkConfigurationToInstall('theme', 'potent_allure') (Line: 216)
Drupal\Core\Extension\ThemeInstaller->install(Array) (Line: 225)
Drupal\system\Controller\ThemeController->setDefaultTheme(Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 580)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 169)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 81)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 58)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 718)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

& when I installed theme in Drupal 10.1.x. it's successfully installed.
Please guide as if I am missing any steps to reproduce this issue.
I am sharing a screenshot for your reference.
Thank you.

Patch #6 Worked well. But the issue is still there, There were four occurrences of the issue.
I have applied #6 patch and fixed the remaining as well. Created an MR !1.

Please review and merge.
Thank you.

Tested with the changes in MR !1, and it fixes the spaceless issue.

Tested MR 1 it's fixed,

User error: Twig\Error\SyntaxError: Unknown "spaceless" tag. in /app/web/themes/potent_allure/templates/form/select.html.twig:13 Stack trace: #0 /app/vendor/twig/twig/src/Parser.php(83): Twig\Parser->subparse(NULL, false) #1 /app/vendor/twig/twig/src/Environment.php(491): Twig\Parser->parse(Object(Twig\TokenStream)) #2 /app/vendor/twig/twig/src/Environment.php(519): Twig\Environment->parse(Object(Twig\TokenStream)) #3 /app/web/core/lib/Drupal/Core/Template/TwigEnvironment.php(131): Twig\Environment->compileSource(Object(Twig\Source)) #4 /app/vendor/twig/twig/src/Environment.php(351): Drupal\Core\Template\TwigEnvironment->compileSource(Object(Twig\Source)) #5 /app/vendor/twig/twig/src/Environment.php(312): Twig\Environment->loadTemplate('__TwigTemplate_...', 'themes/potent_a...') #6 /app/web/core/themes/engines/twig/twig.engine(53): Twig\Environment->load('themes/potent_a...') #7 /app/web/core/lib/Drupal/Core/Theme/ThemeManager.php(372): twig_render_template('themes/potent_a...', Array) #8 /app/web/core/lib/Drupal/Core/Render/Renderer.php(436): Drupal\Core\Theme\ThemeManager->render('select', Array) #9 /app/web/core/lib/Drupal/Core/Render/Renderer.php(449): Drupal\Core\Render\Renderer->doRender(Array) #10 /app/web/core/lib/Drupal/Core/Render/Renderer.php(449): Drupal\Core\Render\Renderer->doRender(Array) #11 /app/web/core/lib/Drupal/Core/Render/Renderer.php(204): Drupal\Core\Render\Renderer->doRender(Array, false) #12 /app/web/core/lib/Drupal/Core/Template/TwigExtension.php(474): Drupal\Core\Render\Renderer->render(Array) #13 /app/vendor/twig/twig/src/Environment.php(361) : eval()'d code(77): Drupal\Core\Template\TwigExtension->escapeFilter(Object(Drupal\Core\Template\TwigEnvironment), Array, 'html', NULL, true) #14 /app/vendor/twig/twig/src/Template.php(394): __TwigTemplate_64a29fbe319dd9445ff04bb091ab0d4b->doDisplay(Array, Array) #15 /app/vendor/twig/twig/src/Template.php(367): Twig\Template->displayWithErrorHandling(Array, Array) #16 /app/vendor/twig/twig/src/Template.php(379): Twig\Template->display(Array) #17 /app/vendor/twig/twig/src/TemplateWrapper.php(40): Twig\Template->render(Array, Array) #18 /app/web/core/themes/engines/twig/twig.engine(53): Twig\TemplateWrapper->render(Array) #19 /app/web/core/lib/Drupal/Core/Theme/ThemeManager.php(372): twig_render_template('themes/potent_a...', Array) #20 /app/web/core/lib/Drupal/Core/Render/Renderer.php(436): Drupal\Core\Theme\ThemeManager->render('field_multiple_...', Array) #21 /app/web/core/lib/Drupal/Core/Render/Renderer.php(449): Drupal\Core\Render\Renderer->doRender(Array) #22 /app/web/core/lib/Drupal/Core/Render/Renderer.php(449): Drupal\Core\Render\Renderer->doRender(Array) #23 /app/web/core/lib/Drupal/Core/Render/Renderer.php(204): Drupal\Core\Render\Renderer->doRender(Array, true) #24 /app/web/core/lib/Drupal/Core/Render/Renderer.php(160): Drupal\Core\Render\Renderer->render(Array, true) #25 /app/web/core/lib/Drupal/Core/Render/Renderer.php(583): Drupal\Core\Render\Renderer->Drupal\Core\Render\{closure}() #26 /app/web/core/lib/Drupal/Core/Render/Renderer.php(161): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure)) #27 /app/web/core/lib/Drupal/Core/Render/Renderer.php(175): Drupal\Core\Render\Renderer->renderPlain(Array) #28 /app/web/core/modules/big_pipe/src/Render/BigPipe.php(693): Drupal\Core\Render\Renderer->renderPlaceholder('callback=commen...', Array) #29 /app/web/core/modules/big_pipe/src/Render/BigPipe.php(547): Drupal\big_pipe\Render\BigPipe->renderPlaceholder('callback=commen...', Array) #30 /app/web/core/modules/big_pipe/src/Render/BigPipe.php(305): Drupal\big_pipe\Render\BigPipe->sendPlaceholders(Array, Array, Object(Drupal\Core\Asset\AttachedAssets)) #31 /app/web/core/modules/big_pipe/src/Render/BigPipeResponse.php(112): Drupal\big_pipe\Render\BigPipe->sendContent(Object(Drupal\big_pipe\Render\BigPipeResponse)) #32 /app/vendor/symfony/http-foundation/Response.php(423): Drupal\big_pipe\Render\BigPipeResponse->sendContent() #33 /app/web/index.php(20): Symfony\Component\HttpFoundation\Response->send() #34 {main} in Drupal\big_pipe\Render\BigPipe->sendPlaceholders() (line 554 of /app/web/core/modules/big_pipe/src/Render/BigPipe.php)
#0 /app/web/core/includes/bootstrap.inc(164): _drupal_error_handler_real(256, 'Twig\\Error\\Synt...', '/app/web/core/m...', 554)
#1 [internal function]: _drupal_error_handler(256, 'Twig\\Error\\Synt...', '/app/web/core/m...', 554)
#2 /app/web/core/modules/big_pipe/src/Render/BigPipe.php(554): trigger_error('Twig\\Error\\Synt...', 256)
#3 /app/web/core/modules/big_pipe/src/Render/BigPipe.php(305): Drupal\big_pipe\Render\BigPipe->sendPlaceholders(Array, Array, Object(Drupal\Core\Asset\AttachedAssets))
#4 /app/web/core/modules/big_pipe/src/Render/BigPipeResponse.php(112): Drupal\big_pipe\Render\BigPipe->sendContent(Object(Drupal\big_pipe\Render\BigPipeResponse))
#5 /app/vendor/symfony/http-foundation/Response.php(423): Drupal\big_pipe\Render\BigPipeResponse->sendContent()
#6 /app/web/index.php(20): Symfony\Component\HttpFoundation\Response->send()
#7 {main}

It's resolved above issue.

RTBC +1

Thank you For Contribution.