Nope. I was actually able to get it working the other day after ditching flatpak and re-installing Steam, Gamescope, and MangoHUD with DNF instead. All the guides I read said that flatpak would be no issue, but it was clear that as soon as I referenced any of the above applications in the launch arguments it would fail to load because it didn't understand what I was asking to launch.
So, all in all, I now have Rocket League running at a high framerate with FSR on integrated graphics. It only took two days :P