My current MPV config is here (in the NixOS syntax but it should be understandable). The profile is what applies the SDR->HDR effect, only if the video is in SDR.
I have target-peak set to 550 nits which seems okay, but I have control + scroll wheel bound to turn it up and down. If you go to 200 or below it seems to disable the effect, which is good for 2D animated content. I also generally turn the saturation up to like 15 or 30 or something since it can look washed out. Gamma looks best at 0 generally, but in dark scenes to combat blooming I might turn it up to like 5 or 10. I haven't messed too much with the tone mapping curve but I'm using what the documentation says is recommended so it seems good.