Anyway to combine TSR (Temporal Super Resolution) with FXAA for better results? TSR looking good so far, although slight edge shimmering is still apparent on the distance; adding FXAA on top of TSR may help to resolve this problem, I guess, or I am I asking a stupid question?
Hmm… I am not really sure if that is possible. At least not by traditional means… I suggest you look here as it will most likely answer your questions: Anti Aliasing and Upscaling in Unreal Engine | Unreal Engine 5.1 Documentation
Hopefully someone else can chime in on the subject! 
All FXAA does is blur an image. Most if not all anti aliasing methods have some downside, quality loss, flickering or other glitchyness. You could run one over the other, even through post processing but all it would do is distort the original source even more. If it’s for a game it’s best to let players pick their favorite method themselves, unreal supports a few out of the box. If not you get the “flickering game” or “blurry game” complaints which is totally understandable. Take fallout 4 for example it was disastrous.