Hi. It's UI bug.

UI app stuck and interface never appear. I see it load my CPU for about 15%.
Tray icon of opensnitch appear as blank area and does not open even menu by click.

I tried to start it from source using cd ui/bin && mv opensnitch-ui opensnitch-ui.py && python3 opensnitch-ui.py and there was some errors with theme module.

I guess it may be somehow related to new libadwaita and that they dropped ability to use user themes.

I don't know how to get you more info. Please tell me how and I will do it.