Errors on input forms, can't uninstall, WSOD.

Steps:
->Check for Existing Content:

Run a query in the database to find any content or entities related to file_resup.
Manually delete any file_resup content if found.

-> Clear Caches

-> use the Clean Files Entity module to remove any ghost entities.

-> Try uninstalling via the admin interface or using Drush.
drush pm-uninstall file_resup -y

-> After uninstallation, delete the module files from /modules/contrib/file_resup

-> Check Drupal logs for details about the error.

-> Rebuild node access permissions to ensure everything is working.
drush php-eval 'node_access_rebuild();'

Hi @zartab farooquee thanks for the guidance. I'll go through these steps.

One question though, when you mentioned "Manually delete any file_resup content if found" what exactly is that content? It should not be that nodes, for instance, have to be deleted in order for file_resup to be uninstalled, right?

Does file_resup create entities itself? This part of the errors seems to imply that:

file_resup: There is content for the entity type: File Resup. <a href="
  

Thanks again!

This issue occurs when you switch the field widget from file resup to another widget. When editing an entity that previously used the widget, a string of errors occur:
Warning: Trying to access array offset on value of type null in Drupal\file_resup\Form\FileFormAlterBase::managedFileProcess() (line 68 of /var/www/***/modules/contrib/file_resup/src/Form/FileFormAlterBase.php)

Warning: Undefined array key "upload_button" in Drupal\file_resup\Form\FileFormAlterBase::managedFileProcess() (line 68 of /var/www/***/modules/contrib/file_resup/src/Form/FileFormAlterBase.php)

Warning: Undefined array key "#upload_location" in Drupal\file_resup\Form\FileFormAlterBase::managedFileProcess() (line 59 of /var/www/***/modules/contrib/file_resup/src/Form/FileFormAlterBase.php)

Warning: Undefined array key "#field_name" in Drupal\file_resup\Form\FileFormAlterBase::managedFileProcess() (line 58 of /var/www/***/modules/contrib/file_resup/src/Form/FileFormAlterBase.php)

Warning: Undefined array key "#cardinality" in Drupal\file_resup\Form\FileFormAlterBase::managedFileProcess() (line 53 of /var/www/***/modules/contrib/file_resup/src/Form/FileFormAlterBase.php)

Warning: Undefined array key "#upload_validators" in Drupal\file_resup\Form\FileFormAlterBase::managedFileProcess() (line 52 of /var/www/***/modules/contrib/file_resup/src/Form/FileFormAlterBase.php)

I've tried to manually disable the module in the database, as Drush cannot uninstall it due to the mysterious file_resup entities, but that doesn't get rid of the errors, strangely enough.

I think this issue deserves a higher priority since it breaks functionality when changing the widget.