That's it, it will never bother you again, unless you turn it back on or reinstall the OS from scratch. If macOS is still too limiting, you can also turn off System Integrity Protection, at which point you can do just about whatever the heck you want.
I personally kept both Gatekeeper and SIP turned off, back when I used modern macOS. But if they are turned on, they ought to work.
No, this still keeps some gatekeeper checks, popups when downloading files, weird arguments being passed to apps on first launch, etc. Even if doing it in the root recovery mode.
I don’t use Big Sur but I don’t think it has any affect on logs. Without SIP, you could patch the kernel or something and change whatever you want, but that would of course be nuts.
I share your curiosity. If your computer isn't already managed, installing an MDM profile in order to view logs is ridiculous. I don’t even think there’s a way to do it without paying money.
That page is somewhat misleading. MDM is one way to install configuration profiles, but you can also install them by hand. No signing required, either. You can just stick that XML in a file with extension .mobileconfig, then double-click the file, and it will prompt you to install it.
Or download a signed version from here (not my site):
That has nothing to do with log redaction. That's to prevent private data escaping apps and either being sent to Apple or readable by others. You want that on.
That I can't answer. The most recent version of macOS I've used for any length of time was High Sierra, because even Mojave broke something essential for me—Apple Events need to be authorized once for every combination of (1) the app being controlled and (2) the app sending the event. Combined with the fact that my authorizations were often reset when I edited a script, this made most of my Applescripts effectively useless.
But it's a very different problem from Gatekeeper. And from iOS, where the user legitimately has no control. If SIP is turned off, you could write an app that strips out every macOS behavior you dislike, because without SIP apps can patch whatever they want.
I personally kept both Gatekeeper and SIP turned off, back when I used modern macOS. But if they are turned on, they ought to work.