NOTE: I no longer rely on this procedure, as I've become more concerned about data corruption than privacy risks. But I also now only travel with a machine that has been privacy hardened and scrubbed of most private data, relying on secure cloud storage (Proton Drive) to retrieve any sensitive materials I may need.
Open source fscrypt provides native encryption for ext4 filesystems on Linux. With it you can encrpyt folders within a disk partition, including user folders. It cannot encrypt files in place, so data must be backed up before proceeding.
The process described below has only been tested on Ubuntu 22.04 LTS Desktop after install and user home creation. All device filesysystems are ext4. The /home directory is mounted on its own dedicated partition (e.g., "/dev/sda3"). I'm doing this to secure the personal data on a laptop from common theives, not state actors or anyone who can get access to the machine while it's running. Your Mileage May Vary. Because.