Alright, did some research with the idea that the 1709 Win10 update might be the issue, and found a very telling response on their own forums: https://answers.microsoft.com/en-us/windows/forum/windows_10-performance/my-screen-is-flickering-after-upgrading-to-the/94fd7fe8-ce57-4dee-9bbe-c5a3779eb8e4
A lot of users seems to be having identical issues as I am with a nearly identical system, but not just on Retroarch (so maybe I’m actually lucky in that respect.) One says:
Same problem here. Using nvidia geforce 1070 with the latest drivers. During the update when windows restarts and is at 30% updated, the screen starts to flicker at a high rate. When the update is done, the screen is almost unreadable, pixleated, flickering, and the color completely messed up.
Changing the resolution to something other than recommended and then back sometimes fixes it temporarily, but it randomly reverts back to broken. Reboot doesn’t help, just puts it back to messed up.
Running on a Asus Z270 motherboard and an intel i7-7700k processor. Recovering windows to the previous version fixes it. Tried it twice, same result each time.
This is frustrating, as there are things in this update I want. I’ve paused updates, but I’m concerned that Windows will eventually force the update on me without fixing this issue, rendering my computer unusable.
For anyone else out there dealing with this issue, it appears that rolling back the update is the only fix at this moment. This issue is on Microsoft’s lap and until they fix it on their end, we’re SOL.
EDIT: More testing after rolling back the Win10 update shows a new issue: my video output completely stops for as long as Retroarch remains fullscreen. So now it’s a complete blackscreen with no sound or anything, as if the HDMI itself is no longer receiving any signal.
TEMPORARY FIX: Change the “size of text, apps, and other items” in Windows settings to LESS than the recommended. Upon restarting your system, the issue will be back, though. So you’ll have to change it again every time you restart the computer.
Really, really, REALLY odd. But at least now I can get it in fullscreen at all.