So apparently, #Ubuntu 24.04 no longer supports installing to an encrypted disk. It's just not an option in the installer. You have to install an earlier version and upgrade, or do some convoluted remount dance to sneak it in.
This is Ubuntu LTS. How can they claim it's business-ready and secure when they *remove* basic security configuration?
Apparently it's something to do with the new installer framework, but I don't care. This is embarrassing.