Module development and code questions

I'm creating a new module to handle searching, I have other modules like this. But when adding the new module I have run into an issue where the others have not. When first installing the module the content appears and then maybe after 20 minutes or so it disappears with the 'hook_theme not found' error. Clearing the cache brings the content back for another 20 or so minutes, rinse and repeat.

Controller:

Hello. 

How I may change drupal field state with ajax request, 

Drupal 9 ajax field set and unset with ajax. 

When user change o fill an field other field need to unset o set, not simply hide. 

Thanks for help. 

As the migration from Drupal 6 doesn't works: https://www.drupal.org/project/drupal/issues/3306744

I'm trying to rebuild the Comment type operation, this is my yml file:

Hello everyone, I'm new to drupal and I need to do something that may be very simple but I haven't found how to do it, I have a list type field in a content and I need to fill it with some data depending on a text field that I send as a parameter to the backend.

I need to know how to connect to the backend to fill that list and how to pass that parameter that is also in the content

Thank you and sorry if it is something very simple