Great—thanks for confirming. On Windows 11 24H2 the “Custom scaling” UI is easy to miss and sometimes doesn’t show if a value is enforced. Your registry reset (Win8DpiScaling=0 and removing LogPixels) re‑enabled true per‑monitor scaling, which is why it’s now behaving.
Do this to finish up and keep sizes matched:
- Set per‑monitor scale (don’t sign out between changes):
- Settings > System > Display.
- Click the 42" 3840×2160 display → Scale: 100% (Recommended).
- Click the 16" 2560×1600 laptop display → Scale: 175% (this best matches the physical size of the 4K screen at 100%; try 150% if you prefer smaller).
- Make sure each display is at its native resolution (Display > Advanced display).
- If any apps look blurry when moved between screens, enable “Fix scaling for apps” under Display > Scale (name can vary slightly in 24H2).
If it ever reverts again, recheck the same registry keys, or use this PowerShell one‑liner to reset and sign out:
reg add "HKCU\Control Panel\Desktop" /v Win8DpiScaling /t REG_DWORD /d 0 /f & reg delete "HKCU\Control Panel\Desktop" /v LogPixels /f & shutdown /l
Need help dialing in exact parity between the two screens? I can suggest a scale based on your exact viewing distance, but 100% (4K 42") + 175% (16" 2560×1600) is the closest match for most setups.