I've enabled full hard drive encryption on all of my devices.

The only exception is my homeserver (mainly running Nextcloud), where all of my personal data is stored.

I'm the only user and have chosen a very strong root- and user password.

From what I've researched, the only person who can see my data physically is the super user (aka. me), but if someone else doesn't have the password, they can't read anything critical and my personal data are safe from the eyes of others.

Is that correct? If it is, why does LUKS exist?