After nearly 13 years, Microsoft seems to have addressed an oft-ignored issue when it comes to how Windows deals with multi-monitor refresh rates. Till now, Windows 10's Desktop Window Manager (DWM) caused stutters and frame-skips when running multiple monitors with mismatched refresh rates. Windows 10 2004 20H1's DWM, which supports hardware-accelerated GPU scheduling in WDDM 2.7, finally seems to have corrected this issue as demonstrated by a user on Reddit.
https://www.notebookcheck.net/Windows-10-2004-20H1-finally-gets-multi-monitor-refresh-rates-right.454143.0.html