Yep, python 3 won’t do as far as I’m aware and there doesn’t seem to be much development done to get it ported/rewritten for python3. There’s an old and long thread about this here on pixls.
I know there’s a flatpak version, which would circumvent the python version thing:
~ $ flatpak search displaycal
Name Description Application ID Version Branch Remotes
Display? Display calibration and profiling with a focus on accuracy and? ?.displaycal.DisplayCAL 3.8.9.3 stable flathub
Haven’t tried that one myself (I’m still on python 2.X), but it might do the trick for you.