Integer Scaler (https://tanalin.com/en/projects/integer-scaler/) will allow you to upscale. Nothing to install, just downlopad the relevant .exe & run it. No system impact. Quicker & easier than changing the entire system res in order to click a few buttons in Immunet. Not perfect but much easier & works.
Quick user guide:
Select & run either x32 or x64 .exe for Integer Scaler
Open Immunet
Hit Al + F11
Carry on as normal...