Unless I’m missing something, Gentoo uses out of tree kernel modules. https://wiki.gentoo.org/wiki/ZFS#Installation
Ubuntu actually bakes it into the kernel for you. I prefer having it in the kernel after having to deal with failed kernel upgrades several times in a row.
Considering that installing ZFS is optional even in Ubuntu, that just cannot be true. Out of tree means that upstream kernel.org does not bundle ZFS.
Btw, Ubuntu 21.10 corrupted ZFS partitions. Their QA is shit.
Keep in mind, Ubuntu rolls it’s own kernel based on kernel.org release.
Pretty sure optional means optional to use as your FS but not optional on your kernel.
Good to know! I’ll double check my version, then again, I skipped the installer and did things the advanced mode for my install so I might get to skip that issue.
