If I try to boot normally, it just hangs on the purple screen and doesn't get to asking me for my disk encryption password.
If I go to "Advanced Ubuntu Options" (or whatever it's called) in GRUB, and try to boot with the 5.3 kernel I see the error
[ 0.794343] [drm:drm_calc_timestamping_constants [drm]] *ERROR* rtc 66: Can't calculate constants, dotclock = 0!
the error number seems to change every time, but the error message is the same.
If I boot 5.3.0 in recovery mode, it seems to boot to the read only filesystem just fine, but when I ask it to continue the boot process it hangs with just a blinking underscore right away.
I can use my system just fine if I chose to boot it with the old 5.0.0-32-generic kernel through GRUB (I'm typing this bug report on "Ubuntu 5.0.0-32.34-generic 5.0.21").
During the upgrade I got an error that it couldn't start sshd because it was already running on port 22.
I've tried reinstalling the latest kernel with
sudo apt install --reinstall linux-generic but that didn't help.