Module development and code questions

Hi! I have a site, and when i click on flush cache, the site is loading old css. It creates a new css file, with the old css, and the last file with the latest css version, just lies next to it in the same folder with a different name.

I've problems setting cookies,   cookies are sometimes set and visible in the browser. But not  by code. I'using a form to set. I see a lot answers, but what is the correct way?

use Symfony\Component\HttpFoundation\Cookie;
use Symfony\Component\HttpFoundation\Response;

       This methods, the cookie is set but NOT visible by $_COOKIE

        user_cookie_save([$cookiename => $cookievalue]);

or
       setrawcookie($cookie, $password, time() + (86400 * 30), '/');

good morning

I am making a website in Drupal8 and I need to add an option to run an app that I would have on the phone to make payments online.

They would know how to do that and if they have any docs on it

I have a simple jquery call in my custom module to dynamically change the css depending on the visitor. The first uses find() of a class in a header and it seems to work fine. Now, I need to find another set of elements in a sidebar but it's not working. When I first was watching it move through my function I saw that the sidebar was processed well after my script had run. That leads me to think to use .once() for both calls but the second ends up changing the sidebar height to 1px.

I want to store some data that is related to a node and trying to figure out the best way of doing it. For example, I send emails related to a node and I want to save details such as:

• To Email address
• Cc Email Addresses
• Date sent
• User
• Email type
• Other chosen email options etc

In the past I would use Paragraphs to have an unlimited field but this will, over time, grow to have a lot of entries. I'm also using Revisions on the node so I think this will slow everything down when saving the node.

I have a node that has a Paragraph field. It has around 80 Paragraphs referenced to it. When I save the node programmatically it's very slow. It seems like the slow down is happening in the preSave() of the field. I'm wondering if every referenced Paragraph is being loaded when the node is being saved?

Could it just be bad design by myself that I created a node that has a field with 80+ Paragraphs referenced to it? Or is it legitimate to do it this way?

I should add that the node uses revisions.