FSE Optimization remains a mystery to many. I also know that some Unity-engine-based games, like Pillars of Eternity, do not even support FSE and that disabling FSE in DirectX 9 games also disables G-Sync.
KEGA FUSION WINDOWS 10 FULLSCREEN DRIVERS
If custom resolution is the only DWM-Sync-forcing scenario then it may be up to NVidia drivers to fix the problem, may not even be Windows-related. They have Sync experts and they go deep into those discussions. MonarchX wrote: Your best bet would be to ask about this on BlurBusters forums.
KEGA FUSION WINDOWS 10 FULLSCREEN INSTALL
In NTLite you need to have 2 main components removed before OS install - Game Explorer (from Media) and Xbox (System Apps). Even Windows 10 1607-14393 had KnownGameList.bin file and game-related DLL files that would hook onto File Explorer, detect whichever games you're playing, and enforce some settings. I would also suggest to make a clean Windows 10 install with all Game-related crap removed and only NTLite (free version) can do it cleanly. Luckily, there's always Windows 1607-14393 without FSE Optimization. On BlurBusters I posted a link to some MS tutoring videos that go into detail about the new "flip" methods in DWM and FullScreen, etc., bla bla.
It does something with mouse sensitivity and I can't even explain what it does. Your best bet would be to ask about this on BlurBusters forums. Please Log in or Create an account to join the conversation. I will post more info if I figure out anything. I've already posted about these issues on Geforce forums but like always, Nvidia won't be bothered to fix anything. Then again, it's windows 10's and Nvidia's fault for not fixing their shit. I don't know if it can be fixed, hopefully it won't be that hard. But downsampling using custom resolution is a lot better since the filtering method by DSR is garbage and only looks okay on 4x multiples of the native resolutions. However, Nvidia DSR doesn't suffer from this issue. So far, the only way to use Scanline Vsync/ Adaptive Vsync on Fullscreen with downsampled resolutions is by disabling FS Optimization but that means Reshade can't be used. But it defeats the purpose of scanline sync. It is possible to at least prevent the stutters by enabling Vsync and using FPS limiter to even out the frame times. Also, since it doesn't work like regular Vsync, the frame times aren't synchronized and results in microstutters/ skipping and stutters just like Fast sync. Windows 10's DWM takes over and prevents screen tearing on games but unlike regular Vsync, windows 10's DWM works like Open Gl's Triple Buffer/ Nvidia's Fast sync but adds severe input lag. Unfortunately, if Fullscreen Optimization is enabled, then scanline Vsync doesn't work with downsampled resolutions. This new syncing method allows users to get adaptive vsync experience without the input lag of adaptive vsync. Now I know something's wrong with the latest version of Windows 10 that make's reshade incompatible with Fullscreen optimizations disabled and you might wonder why do I want to even disable FS Optimization.