Exposed filter with multiple selections allowed generates error "Input value contains a non-scalar value"

Thanks for reporting this.

I tried to reproduce this with a clean Umami install of Drupal.
Steps:
* Added a View containing content with a page display
* Added a 'content type' exposed filter with 'Allow multiple selections' and 'Limit list to selected items' enabled
* Saved the View
* Went to the page showing the View
* Filtered on 2 content types
* Filtering worked, no errors

Am I missing some steps to make this break? The screenshot appears to use a Search API View and index as it's source. Is this really a Drupal core issue or something that needs Search API to reproduce?

Iam also getting similar issue while migrated my website to Drupal 10, My views have exposed fields with multiple selections allowed. in exposed fields i have taxonomy terms. If I deactivate the ajax option, the view returns nothing and generates an error. The error in the logs is as follows:

Symfony\Component\HttpKernel\Exception\BadRequestHttpException: Input value "type" contains a non-scalar value. in Symfony\Component\HttpKernel\HttpKernel->handle() (line 83 of /app/devs/vendor/symfony/http-kernel/HttpKernel.php).

Steps to reproduce
See attached screenshot.

I had the same issue, i did some digging, and I discovered that the filter key was conflicting with some other functionality.

In my case: I had a multi-language website, and the Language Negotiation was based on the language query parameter, but my exposed filter also had the "language" filter key. I changed that to "lang", and it's working properly.