Issue running on a 4k monitor scaled to 1080p (Both mac and windows

I have an issue running league on a 4k monitor downscaled to 1080p on both mac and windows (bootcamp). On mac it sets the monitors refresh rate to 24Hz and on windows the fps has frequent drops. None of these issues were/are present when I use an actual 1080p monitor.

The issue goes away on mac if I used borderless window mode (but then I get locked into 60fps)