When single user mode works but it crashes when booting normally it's often a kernel module that's causing it. You can get into a situation like this when loading a 12.0 kernel module on 12.1 for example. To rule those out look in your /boot/loader.conf and remove any additional modules you may be loading there. Then see if it can boot normally without them.
Have a look in /var/crash/. But you may only have a core dumped there, which is not that interesting and requires quite a bit of technical wizardry to make sense of those. Usually I don't bother with them, I'm not a kernel developer so it's all abracadabra for me anyway.
That's weird. As that would more or less imply it's ZFS that's causing the crashing. Are you using a custom kernel? And speaking of kernels, what version of FreeBSD? Did you do an OS upgrade recently (packages don't count, ZFS is part of the OS)?
kld_list in your /etc/rc.conf? Try disabling it if you have. As for the rest of /etc/rc.conf, disable as much as you can, but leave the important things like IP address and sshd(8). Try to get it as basic as possible. If that works you can, one by one, enable things again until it starts crashing. Then you know the last thing you enabled is likely the culprit.
Ok, good, that's the issue. The graphics/drm-kmod package is still being built for 12.0. And you now have 12.1. So that's the cause of the crash.
Yes, that could possibly have happened if there was a new version. A pkg-upgrade(8) would install the new version from the package repositories.
