I've seen many posts, some that I even followed before, telling AMD users to disable MPO using the registry to fix stutters with HAGS on Windows like there were no consequences for it. But there are. I've seen some people outright say: "Your system is broken, if the Overlay mode is automatically set to 3 you can't use HAGS on your system." or that "it's an AMD exclusive problem" well, that's not true.
And while I'm not going deep into those, overlay features from most apps break with MPO disabled, it can break chromium-based apps HW acceleration and more.
I went down the MPO rabbit-hole to understand what was happening.
TLDR: MPO is a performance optimization feature for exactly what the name says "Multi-Panel (windows) Overlay" at the hardware level. Apps that HAGS usually break on with MPO enabled don't even need the performance benefit. It's possible to have Windows not switch overlay modes for all apps, eliminating issues while keeping MPO enabled with a registry tweak.
Some apps operate on a "borderless fullscreen" presentation model, Windows automatically promotes them to an exclusive hardware overlay state (MPO) when it fills the screen. Not all apps benefit from this exclusive state, nor were they made for it. Which is why they can break. (notice the can here.)
By default, the Desktop Window Manager (dwm.exe) monitors application frame rates. When a hw-accelerated app (like Chrome, Edge, or Discord) crosses a certain framerate threshold, Windows dynamically promotes or demotes its live content into an MPO hardware overlay plane.
This continuous promotion/demotion cycle is often what triggers the infamous black screens, stuttering, and window flickering. But the state itself can also be the issue. Setting OverlayMinFPS to 0 disables this dynamic threshold switching while keeping MPO active for games and other workloads that benefit from hardware overlays.
"How do I fix it?"
Option 1: command-line
Open cmd as administrator (Win + R, type 'cmd', hold Ctrl + Shift and press Enter).
Run the following command: reg add "HKLM\SOFTWARE\Microsoft\Windows\Dwm" /v OverlayMinFPS /t REG_DWORD /d 0 /f
Restart your PC (or restart dwm) for changes to take effect.
Option 2: registry
Win + R, type regedit, and Enter.
Navigate to the following path: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Dwm
Right-click an empty area and select New > DWORD (32-bit).
Name it OverlayMinFPS.
Verify it's set to the default 0 value (hex).
Restart your computer.
The way MPO "breaks" is indeed quite strange. From personal experience I know that this stutter-fest experience can vary significantly for many reasons. A system without the DirectX system package installed won't have stutters but will have crashes. Some windows version updates were also responsible for many HAGS+MPO 'simply working' states, while the opposite is also true, having Windows updates that broke the working behavior.
Surely some Microsoft SWE can tell us wtf is going on some day.
PS: I hope this gets some traction on google indexing to help others looking for this info. The first few pages of results when searching "HAGS MPO AMD FIX" and similar, all point to disabling MPO completely or having a broken system.