Taa + fxaa?

Is TAA + FXAA possible to do in UE4?

it’s only possible by modifying the engine source files
if you know your way around the rendering code it’s relatively simple actually

I am not sure what TAA + FXAA is. I assume you are referring to T+FXAA, which is ordinary FXAA, that takes additional samples from previous frames, that were deliberately offset to get you subpixel data. In such case, yes it is possible and there is even source code for that linked somewhere on the forums.

Oh okay do you know some links where i can get my hands on source code for it?

He means this SMAA – Subpixel Morphological Antialiasing integration - Unreal Engine Forums. It has a “bonus” mode which is T+FXAA. There isn’t up-to-date fork for that though, I have ported that repo for 4.18 and 4.20 (4.20 not publicly on my fork) but neither of them work right atm due to missing stencil pass implementation. But you can still use these repos (original 4.14 or my port) to check how the T+FXAA handles the additional passes and try to replicate that on Unreals TAA and FXAA yourself.