Module development and code questions

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

I'm trying to change the text of the "Login failed" flood control page. I can do that but I lose Drupal's maintenance page theme. I get nothing but my new message text. This is what I did:

bncreports.module

I have created a new module for dupal and would like to contribute to the community. The problem is that I don't know how to create the composer command to install the module.

Have someone a tutorial?

Thanks in advance.