Well, thanks for an elaborate answer! Unfortunately, it's not that simple.
Meanwhile, I just tried, and, well, the immediate answer is:
NO. Whole story:
What I found broken was networking (e.g. promicious mode couldn't be set on any interface, breaking all of my bridging) and bhyve (machines booting with uefi couldn't start any more). There's probably more. So, sure, a jail with a 12.2 userland will run fine, but the main userland is a different story
This is a machine with lots of jails and vms doing everything for me at home. I don't want it down for too long, and I definitely can't risk having it broken.
So, as I need a 13.0 userland at least on the host, I tried to install it in a separate boot environment (to have a way back).
make installworld
also installs a few bits in
/boot, and with a separate bootpool, this is "global" for all boot environments. But even worse, I found the loader won't boot my environment, which is probably also because of this:
I installed my server with 11.0-RC1, and back then, the installer created a separate (unencrypted) bootpool for ZFS root on GELI. Now, I know this isn't needed any more for a long time. Are there any instructions around how to migrate an existing installation to get rid of the bootpool? Anything...
forums.freebsd.org
Well, disaster hit me here, cause now, VMs using
bhyveload
also didn't boot any more. One of them is my central router/firewall, so, LAN and internet defunct. It took me a while to realize this must have been broken by the 13
make installworld
installing stuff in
/boot, and yet ANOTHER while to remember I had snapshots from my backups that also included my src and obj trees, so null-mounting THEM as
/usr/src and
/usr/obj, I could finally recover with another
make installworld
.
I guess I'll first have to solve that problem with the dreaded bootpool and get boot environments to work before starting another attempt.