I’ve run the AFMF/FSR3 driver with freesync on & MSFS vsync on (100% of monitors refresh rate) with TAA antialiasing and HDR-10 and had excellent results (@4k with stock ULTRA presets). My monitor is a 55" Samsung Qled running a 120Hz refresh rate.
I think MSFS internal vsync is different from the vsync AMD mentions not to use. Not sure if that answers your question though…