Howard Miller

It is certainly unusual.

For the most part, I am giving him the benefit of the doubt. As the questions are not usually that hard to answer (or point to the answer) and may help somebody else.

I don't understand your question. You hide the category if you don't want anybody to see it and its contents. That's it.

Why you might want to do that is up to you but it's not hard to think of some scenarios.

LMGTFY....

https://docs.moodle.org/404/en/Course_categories#Hiding_categories

It tells you exactly in the highlighted red area what to do.

Find the file config.php in the root directory of your Moodle install, open it with an editor, find the line $CFG->dbtype (near the top) and change mysqli to mariadb.

Don't shoot the messenger

Ubuntu, for example, supports non-LTS releases for only 9 months. So this is reasonably normal.

Don't ask why the support cycle is so short. Instead ask how you can factor in to your workflow doing regular Moodle upgrades.