VN and Big Sur are not getting along well here too. I have a iMac 2017 with Big Sur, latest version installed.
That screenshot you took should be the splash screen of the engine/editor, but it is incomplete, won't load if you don't give full disk access to the game (system preferences > security & privacy > accessibility). Now you should be able to start the editor but you'll get the allow/not allow sys dialog to use the internet network. You MUST click on ALLOW, yep, every freaking time you open it, otherwise it will crash.
Sometimes you may need to go to the Activity Monitor.app to certify that the 'NWJS Helper' does not exists anymore by manually delete/cease it when VN crashes, or else the STEAM version won't be able to shutdown correctly (yep, it will keep eating more sys resources).
I'm still waiting for a true fix for this problem. I hope someone have something better to show us here.
Back home now. I had a good time, but I had a checkup this morning so I had to come home for that. Now I'm just waiting for my therapist meeting tomorrow...
Decided to work on Wishful Wanda today. Since it's a BFB spinoff game, I decided to make the Huang brothers
Easter eggs! I'm actually pitching this to the BFDI team, btw.