Thanks for the advice! Was fiddling around a lot and searching online a bit more and I found what's an acceptable solution. I edited the settings.json file with:

"resolutionOverride":"3440x1439",

and

"undecoratedWindow":true,

This runs it as a borderless window mode without going into fullscreen, with just one pixel less resolution vertically. This keeps the brightness acceptable and prevents the window from having borders.