How do I uninstall RSS? I would like to uninstall RSS completely from Drupal 8, not only hide it from pages, but also disable the core logic behind it.

How do I achieve it?
I am not sure where you encounter RSS, but I am only aware of it being on the front page. That feed is generated from a second display on the frontpage view:



Other modules might define their own feeds in a similar fashion, but I have not found them yet.

There is no such thing as 'disable RSS', so you cannot disable it globally.