Hi pingtoo,
Thank you. Now I understand the mistake. I configured /etc/fstab and boot file according to the manual. The device should be able to boot from Gentoo now, but it keeps booting with Ubuntu Server. I guess something went wrong with the configuration of the boot file. I used the following manual for these two configurations: https://www.famera.cz/blog/computers/ge ... -luks.html
I'll try to figure out what went wrong and I'd love to get your insight as well.

