Framebuffer: I don't think so.
Deflicker: ROM hack. Don't have exact steps but what I understand from
https://gbatemp.net/threads/possible-to-disable-the-wiis-de-flicker-filter.477163/ is that you need to use wiiscrubber to extract the main.dol from the .iso, then hex edit it to disable the deflicker and finally reimport that into the .iso.
Note that I never did this nor did any other Wii ROM hacks, so all I said is highly theoretical.