So, I found out the issue with Cinnamon. The issue SPECIFICALLY is to do with WINE freaking out in full-screen mode when a game (Both DXVK and wined3d) in WINE/Proton goes full screen. Windowed mode seems fine, but full-screen is all sorts of messed up.
They are no closer to a resolution, so if you game in full screen a lot, switch to KDE if you plan to also stream/record at the same time. This is going to go unsolved for a VERY long time.
Edit: They attempted a patch to Muffin in Muffin 4.0.6 but that did not solve the Xcomposite issue with OBS, nor did it solve the FreeSync issues.