TypeError: implode(): Argument #1 ($pieces) must be of type array, string given in implode() (line 29 of /app/web/core/lib/Drupal/Core/Form/FormElementHelper.php)

The patch for the <strong>FormElementHelper</strong> has been provided.

Thanks for providing steps. Have not a full change to verify but this seems like a larger issue could be at work.

But as a bug will need a test case.

the numbering on the patch is wrong. but it fixed the problem for me.

Hi The patch #2 fixes the issue on media library for alt text. but as mentioned in #5 the patch name is not correct. updated the patch.

Thank!

Ran into an issue today that triggered this for us in Drupal 10. Patch from #6 fixed the issue.

Created a MR from patch #6
MR: https://git.drupalcode.org/project/drupal/-/merge_requests/8297
Branch: 3353388-type-error-implode

I have reached this issue after having the same error using Inline Entity Form. The error appeared when developing a custom validation via "#element_validate", specifically when I called the setError method. I mention it in case it would be interesting that the test also covered this case. The path #6 fixes the issue.