How (if) can I have a permanently writable system volume in Big Sur?

From Mojave to Catalina to Big Sur

Earlier this month I upgr– Not that. I changed my system to Catalina, I had been using Mojave, as I expected, I really didn't like it much. However, at least it turned out I would be able to keep writing to my system volume like I had in Mojave, so I kept it.

I'm still not a fan though, one of the first party apps I used the most which already was far less than perfect, got replaced by two (or twenty, I don't know. Those were the first I deleted.) apps way worse in every possible way. So I figured, it I'm already using a system that I don't like, I might as well continue testing newer ones, hopefully at least that way I gain a little compatibility with various apps again.

SIP + GateKeeper

I installed Big Sur on a guinea pig MacBook Air, it's noticeable slower, but I switched around Tiger, I've had time to learn a thing or two; it's probably just indexing + the age of the low power CPU. A new directory of replaced stuff appeared on the desktop, first I thought it was the same one from Catalina. Among the sluggishness and various warnings, and Aqua out of sight, I had a bit of a hard time getting to a CLI, when things seemed to start populating in Spotlight, an extension popup got me out of there and into the panel showing that GateKeeper was turned back on. Not really surprising.

SIP was still off though, I learned when I finally got a CLI. I turned GateKeeper back off. No warnings, no issues. I allowed the extension after that and only then it prompted me to reboot.

Once back in the system, I made a little modification to the sudoers file. I was among the replaced files. Surprisingly it went through; I had read something the system self-reverting or refusing to boot. A quick check of diskutil and sure enough there was a snapshot in there. I rebooted before investing more time in it to see what would happen, it seems nothing. Yet, at least. The modified file remained.

Unsealed volume

I assume I have an "unsealed system volume". Is that possible? All I had read beforehand pointed in the opposite direction, and let me to believe I would have to create snapshots all the time for the tiniest mods, but mods so far have stayed put.

Can macOS with this type of disk can be used mounted permanently writable? On one hand it appears to be true, on the other, remember that extension? That wasn't supposed to be compatible beyond Catalina but since I installed over an existing system, I think it may have done an exception (or more), such as [another would be] keeping the launchd service that remounts the system volume as writable, which I created and installed back on Catalina.

Could you confirm which of this things is true or false or neither-but-you-have-some-advice-and-show-me-a-d-pic? (I mean… if you gotta do it you gotta do it, I understand.)

I really don't know if I want bad news or good news. Good news, would be, well...good. But bad news wouldn't be that bad because it would make it so much easier to quit macOS for good. I still use it only because of a third party design app, the system itself together with iOS has been ruined by Apple, thus I stopped purchasing Macs, meaning knowledge gained won't be transferrable beyond the remaining life of my existing devices.