Module development and code questions

I'm building a custom module to be used to modify the general layout for my site, specifically for a landing page and splitting the site into some major sub-sections that are themed slightly differently. To do this, I'd like to hide certain regions and blocks from these particular routes/pages.

I'm having trouble finding a way to access a list of regions and then unsetting them programmatically. I found some forum answers to similar questions that use something like this:

What i need to ask if it is possible to login into drupal with users from another system ,but the point is that i do not need to register these users as drupal users , is it possible or i should register the accounts into drupal ?

Hi, the issue I'm having is the the is-active class isn't set on the <li> for the active language in the language switcher. This only seems to happen after I write a value into the session:

\Drupal::request()->getSession()->set(self::SESSION_KEY_DIN, $userDin);

This seems to happen with any session key, not just the one in this example.

Hi, I'm working on moving from D7 to D10 a module that adds a specific display for entity reference fields (i.e. to print first + last name rather than login for users, and other things related to our contents).

This part works fine (with a class that extends FormatterBase) but with multivalued fields each value is on a separated line. I tried in the viewElements() to cleanup any classes, or to insert style, or inline classes, but it seems that the DIV prevents the inline to work (DIV field-labels + field-label each).

Hello,

I am new to module development.

I like incrementing the counter using AJAX in the Drupal form, which works. I like to add a reset button to reset the counter, but I am not sure how.

Running Drupal Version 8.9.18. Have set up subscription service in Paypal and want to link buttons to website. Have pasted the Paypal code into a content box and tried again with pasting into the link box but I just get a lot of code and not a button. 
I'm not a programmer so please be very basic in any replies. Also I need to link Paypal to Drupal via an API number but I am not sure where to find it. Can anyone help. Thanks in advance.