I kind of bailed on macOS prior to Big Sur, so I'm not sure—but I think you can do that. Authenticated-root would need to be kept turned off, but that's a separate thing.

You're going to have to redo everything after every update, however.

No it can't. You'd have to disable SIP temporarily in the first place, and a rootkit can't boot a recovery environment while SIP is engaged.

And then on Apple Silicon Macs, entering 1TR is tied to the physical action of holding down the power button.

But you disable SIP while booted in recover mode. Somehow Apple needs to do this anytime the system is updated.