I gave up: Dual monitor,4K + FHD, one of them is blurry no matter what

Hi everyone. I really hope I'll find a solution - I've searched the web pretty thoroughly. Couldn't find any solution.

Problem: Most apps look blurry on the FHD monitor. Every solution brings a new problem to the picture.

I've tried every combination I could think of, of:
- XPE DPI Fix
- Changing the DPI settings for each monitor individually
- Tweaking the "override dpi" setting under "compatibility" for each app individually
- Lowering the 4K monitor's resolution to FHD.

Findings:
Without XPE DPI Fix, having the 4K and FHD monitors to 200% and 100% scaling respectively, and tweaking the override dpi under compatability, results in each app behaving perfectly on the 4K monitor, and most of them behaving blurry on the secondary FHD one.

With XPE DPI Fix on, nothing is blurry but it forces a universal scaling to both monitors, so I end up with either the FHD having gigantic items or the 4K having miniature ones.

There has to be a solution. Any tips are welcome!


Thanks a lot,
Gilad

Sorry, probably hasn't made it clear - I'm assuming there's something that I haven't tried.