Sadly SteamOS doesn't support full disk encryption, which is inexcusable for an OS used on a portable device, that some also use to remote access their desktop (through Steam Link/Moonlight).
It actually does in the upstream dev builds https://gitlab.steamos.cloud/holo/dirlock/-/wikis/Enabling-d...
It’s not in a consumer friendly state yet, but I’ve been using my steamdeck with encryption for a month now with zero issues. I guess technically this is not “full” disk encryption since it’s just the home dir, but I only care about protecting my personal info which is all in the home dir anyway.
It doesn't need to, if your disk supports OPAL2 - just set the password in BIOS and encrypt the drive, it's fully transparent to the OS and as a bonus, there's virtually no performance hit unlike software-based encryption like LUKS.
I personally don't keep anything sensitive on steam deck or heck, any device related to "gaming". Modern games are nothing but spyware and even more reasons if you are pirating
Encrypted home directories are coming to the Steam Deck, using the same kernel API that Android uses. https://lwn.net/Articles/1038859/
FDE would be nice though.