The Ubuntu thing was about them making it opt-out rather than opt-in (so turned on by default), but it’s still nothing malicious and diesn’t collect any personal data. At least that’s how I remember it.
Also Linux doesn’t really have anti-viruses like Windows does (there are a few options for edgecases though). That is because Linux isn’t really targeted by malware developers as much and also Linux is actually designed to be secure.
As for general security tips, number 1 is probably using a password manager (I use a KeePassXC compatible client).
Also be careful with rm -rf. I almost deleted all the files in my home directory once. I have aliased rm to gio trash since.






X11 is the last version of Xorg, not sure what you meant there.
It was configurable and will stay configurable. The intent is to change the default.
Personally I support the change, but that might be because of my adhd making me click on the mouse wheel every 0.1 seconds.