I'm also having this problem - seems to happen to me if I try to change my fullscreen resolution to anything other than my native resolution. My native resolution is 3840 x 2160, but if I try to set the ingame resolution to 2560 x 1440 the game minimises itself and clicking on the taskbar or alt-tabbing cause it to flash up for a few seconds and then minimise it again.
I have all my background apps closed as far as possible, so that's not the issue here. The game isn't handling lower resolutions correctly.
Edit: a possible solution at the moment is to wait until the graphics settings revert themselves (since you won't be able to accept them), then try setting the resolution again. This seemed to work for be, but could be a fluke.
Edit again: unfortunately though, the only way to fix the problem if the settings were already set (and you're just starting up the game again) is to edit the config files.
After more experimentation, closing Discord seems to fix the problem? Although it could just be a random thing again.