I run Arch on mine so I can’t speak to the Gentoo experience, but I can tell you a bit about MORPHIUS. It runs Linux pretty well for the most part, but the embedded controller exhibits very unusual behaviour all the time, so prepare for that. If the battery dies, the laptop refuses to turn on again until I leave it plugged in for about 15 minutes. I also had an interesting adventure just the other day when I was trying to get the backlight adjustment to work properly.
I think the only other really noteworthy thing to mention is that recent versions of GRUB seem to be broken on this device. I was unable to get any Debian 12 installer to boot, and I encountered the same problem when I tried installing Debian 11 and upgrading to Debian 12. I was able to install Arch without any issues since it’s installer uses systemd-boot, which I also highly recommend installing as your bootloader, although I think it should work with anything that just loads the kernel directly as an EFISTUB.
In spite of the few quirks it has, I still really like this laptop and it’s one of my favorite Chromebooks of all time.