I have Gaia 3.0 and 3.1 available too but they are just workarounds for existing installations.
The problem with this theme (or other ones) are plugins they depend on. And those plugins depend on THEME_LAYOUT and it is not available anymore. So plugins don't work and the theme doesn't work fully either.
I asked how to create variable headers with 2.3.1... no answer.
Now, maybe the only solution is to make a simpler new theme with rules for 2.3.1. I will see what I can do.