With modern CPUs and hardware encryption isn’t a big deal. And that extends to far older stuff than you have.
The only system I don’t full-disk encrypt is an e-reader which I just encrypt my home directory with. That was just a matter of created the encrypted location then adding a couple of lines in config files for pam_mount.
For full disk encryption just select it in the installer.
Here’s a step-by-step guide for ZFS that probably still works, but BTRFS/LUKS should “just work”