EDIT for anyone struggling with DPI problems: Windows seems to over-ride the Nvidia control panel's default GPU, at least on my system. Swapping from the integrated graphics to the 'high-performance' Nvidia GPU option in System->Display->Graphics for wsl.exe and wslg.exe seems to have fixed it for me. I can't 100% confirm that was the solution as I was tweaking a lot of other things, but it's my best guess.

EDIT 2: This did not work for a second WSL instance, so there goes that theory. Though it may be necessary along with other steps.