This is not a Windows issue, the problem lies elsewhere. I will try using a modified side-by-side manifest with KeePass. I'll let you know if I discover anything interesting. However I've just created a test app (Delphi) that mimics KeePass, and it runs smoothly with UIAccess enabled. This demo just sends 1234567890 to any window, including elevated ones. https://www.swisstransfer.com/d/d4766634-500d-403d-9677-ff31281d7e51 ps: after running the modified KeePass, I had to reboot. The mess remains...
Add support for apps with a higher integrity level.