Ubuntu allows you to encrypt the system partition when setting up a new machine. This is a good idea if it's a portable device with sensitive information.
Still working on how to use encryption in other contexts.
cross platform drive encryption at DuckDuckGo
VeraCrypt - Free Open source disk encryption with strong security for the Paranoid
Home - FUSE for macOS
20 Best file encryption tools as of 2020 - Slant
GPG encryption and decryption of a folder using command line - Stack Overflow
How to encrypt a USB stick on Linux, Windows or Mac OS
cross platform usb drive encryption - Super User
Cross Platform USB Flash Drive Encryption? - Spiceworks
7zip encrypting files at DuckDuckGo
gpg encrypt directory at DuckDuckGo
bitlocker at DuckDuckGo
An error occurred while setting the recovery key. The installation will continue, but you may have to manually add the recovery key in the installed system with the command: cryptsetup luksAddKey device_name