Can't select more than one checkbox at a time

Try disable caching on your view and see if that helps.

@mkalkbrenner Thank you a lot!
In my case unchecking "Ensure that only one result can be displayed" option solved my problem!

I created a patch to resolve the deprecated Request::get() usage and missing session assignment for D11 compatibility.
The 2 issues addressed in the patch are

1. Symfony Request::get() (deprecated scalar handling).
2. Session not set on sub-request (required in Symfony 6 / D11).

This resolved my issue in Drupal 11 PHP 8.3, where only one checkbox per facet could be used until you refreshed the page. The Specific errors were.

• An AJAX HTTP error occurred.
  HTTP Result Code: 500
  Debugging information follows.
  Path: /facets-block-ajax?_wrapper_format=drupal_ajax
  StatusText: Internal Server Error
  ResponseText: The website encountered an unexpected error. Try again later.
  InvalidArgumentException: Expected a scalar value as a 2nd argument to "Symfony\Component\HttpFoundation\InputBag::get()", "array" given. in Symfony\Component\HttpFoundation\InputBag->get() (line 32 of vendor/symfony/http-foundation/InputBag.php).
  Drupal\facets\Controller\FacetBlockAjaxController->ajaxFacetBlockView(Object)
  call_user_func_array(Array, Array) (Line: 123)

• Symfony\Component\HttpKernel\Exception\BadRequestHttpException: Session has not been set.
  in Symfony\Component\HttpKernel\HttpKernel->handle() (line 83 of /vendor/symfony/http-kernel/HttpKernel.php)

• Uncaught Drupal.AjaxError {
  message: "\nAn AJAX HTTP error occurred.\nHTTP Result Code: 500\nDebugging information follows.\nPath: /facets-block-ajax\nStatusText: Internal Server Error\nResponseText: The website encountered an unexpected error. Try again later.InvalidArgumentException: Expected a scalar value as a 2nd argument to \"Symfony\\Component\\HttpFoundation\\InputBag::get()\", \"array\" given. in Symfony\\Component\\HttpFoundation\\InputBag->get() (line 32 of vendor/symfony/http-foundation/InputBag.php).",
  name: "AjaxError",
  stack: "Error at core/misc/ajax.js"
  }