Aight so this is working again. The only thing I could figure was that because I had rebuilt windows, permissions on the game drive that had Steam installed might have been "wrong", even though I force took ownership of everything after the rebuild. Even though I had already reinstalled the game once, I decided to uninstall Steam and format the drive entirely - then reinstalled Steam, then spent the next 9 hours downloading the game again. Now, it works. The only change was reformatting and reinstalling - I had already, in order: re-installed Windows but left the game drive alone (which includes re-installing nvidia drivers/control panel/etc) re-installed Steam checked game integrity after the first potato error (and a few after) deleted/re-installed the game (9 hours I'll never get back) deleted the installed video drivers via Windows uninstall installed video drivers (gaming version) via NVidia download (not from the windows store or letting windows use their nvidia drivers) wiped drivers with DDU, disabled Windows auto-driver-install and Windows Store app installs (Windows kept automatically "finding the best driver" and Windows Store kept automatically re-installing the Nvidia control panel, even though they were getting over-written by the NVidia installer after anyway...just in case) re-installed NVidia from download, their gaming drivers wiped drivers with DDU again when that didn't work installed NVidia reference drivers instead of gaming drivers Still not working... After all that, my last act was to re-format the gaming drive and reinstall Steam again, and spend the next 9 hours downloading the game again (and now to spend a lot more time downloading the rest of my usually played catalog).