I’m not the person you asked but I hope it’s okay that I take a crack at your questions.
Madaidan has some relevant articles on things like Linux and Android security and how they compare to other systems. I’d warn you that his work might be somewhat outdated and in my opinion he demonstrates some bias against Linux and in favour of Apple/Google/Microsoft.
I provide some justifications for why some would prefer Linux in my earlier answer which itself links to another answer on a different thread.
Most desktop Linux distributions do not share any data without your permission and in that sense they could be considered more private. But when it comes to concerns over cyber threats, things become more complicated and have a lot of nuance. As I mentioned, it’s not like the average Joe needs to fear Linux for not being secure enough in the current day, though that could change in the future if desktop Linux security doesn’t keep up with the pace of its growing market share. Sticking with a recommended distribution (as you have) puts you ahead of most other users.
System hardening is primarily targeted towards system administrators rather than average Joe’s, but there are some guides for it. Even so, “hardening” desktop Linux doesn’t provide it with comparable security features and exploit mitigations to something like macOS. Anyone who’s extremely concerned with both privacy and security on desktop should consider using QubesOS rather than Linux. Due to its strict hardware requirements and usability limitations, many may settle for a security-focused Linux distribution like Secureblue instead.
This point is addressed by PrivSec.