FYI, this solution did NOT fix my issue with the game never staying in fullscreen mode according to the game settings -- even if visually it IS in fullscreen mode.
I did NOT try the Big Sur beta, as I'm not willing to risk that with all the other work I do on my computer, just to play a game.
I DID try turning off the automatic graphics switching toggle and experimented with the game multiple times. The issue simply will NOT resolve itself.
Even if the game looks like it is in fullscreen mode, the in-game setting SAYS windowed mode, and thus the EDGE SCROLLING WILL NOT WORK.
No matter how many times I try to get it to switch to fullscreen mode, it instantly switches back to windowed setting -- even after I have clicked "accept new settings" with the setting saying that "full screen" is selected. The minute I hit "accept changes" it switches back to windowed setting. But the appearance doesn't change. Just the setting does.
Sometimes, and this seems to happen randomly, the setting in the background will say "fullscreen" but the cursor cannot click on the "accept settings" option OR even the "cancel" option! I click and nothing happens until the timer expires and then the settings revert back to windowed.
This is SO FRUSTRATING!
Before this latest game update, I was able to play on this computer without issue WITH EDGE SCROLLING!!!
Do I need to make this a separate question so that it can be addressed properly? Because this workaround did nothing to fix it!
And I was not having any of the other graphical issues. No flashing floors or black lines, etc.
My setup, FYI:
MacBook Pro (16-inch, 2019)
2.4 GHz 8-Core Intel Core i9
32 GB 2667 MHz DDR4
AMD Radeon Pro 5500M 8 GB
Intel UHD Graphics 630 1536 MB
ETA: Yes, I tried playing around with the green fullscreen button on the windowed game several times, and it still says it's in windowed mode -- even after I've expanded it. And I've tried loading the game in windowed mode, and then using the control/command/F trick to expand it to fullscreen. It does VISUALLY, but the game settings still say "windowed" mode, so the game THINKS it's in windowed mode, so the edge scrolling will not work!