Using the pre-installed Ubuntu Desktop 20.10 disk image for the Raspberry Pi 4 (64-bit ARM), you do not get an option to encrypt the disk using LUKS when you install the system, as you do with the x86 USB-based installers.
For reference, I followed the instructions here to get the system installed to an external SSD: https://ubuntu.com/tutorials/how-to-install-ubuntu-desktop-on-raspberry-pi-4#1-overview
In all, I am very satisfied with the install, but I would prefer if I was able to encrypt the whole drive. I don't want to bother figuring out how to just encrypt the home folder, so if anybody know hows to get a 20.10 install encrypted w/ LUKS at the time the OS is installed, I would appreciate hearing how you did it. Thanks!