Greater than 97% with H.264 and possibly HEVC produces a file that is not playable in some media players and is discouraged (same goes for lossless/H.264) unless you understand that limitation. With that said, anything over something like 85% and less than 99% is commonly considered visually lossless if not truly lossless. This means, you are not really gaining much improvement if your goal is to share it on YouTube.
Maybe amf isn’t one of them.
Of course, that depends on your hardware. “amf” for AMD, “nvenc” for NVIDIA, and “qsv” for Intel.