I tried your solution, it worked! Did a dozen times just to be sure, with both 'bg3.exe' and 'bg3_dx11.exe'.
But in my case there was a peculiar thing: in my tests, when I clicked 'Run as Administrator', I had to quickly close the Explorer window, otherwise the game would crash as before.
Well, so far so good.
Thank you and gather your party before venturing forth.
EDIT:
Win 7, GOG Galaxy. Black screen at launch.
What works for me:
1. Hold SHIFT (or any other key) + click Play button from Larian Launcher and keep holding SHIFT until the game loads. (no need to launch from exe, or messing with administrator rights)
2. Click Play button from Larian Launcher and keep fast clicking anywhere within the Larian Launcher window until the game loads in the background.
3. Click Play and keep spamming Alt+Tab until the game loads.
It seems that the game crashes if the game window is focused when launching.
But it works when you keep the game window (out of focus) in the background while it is loading - else by spam clicking, or holding keyboard keys.
Tried this, and worked too. It's hilarious this rascaldom of solutions that is actually the only way to play tha game.
