Recently got the same LG C1. Would you mind sharing what Windows/NVidia settings you played with?
I use TV settings as per HDTV tests C1 and PS5 settings Youtube video, obviously ignoring the PS5 specific bits. I have the TV tone mapping on HGIG. It's a darker overall image but with more contrast between the dark bits and bright bits which is sort of the point.
I leave HDR on in windows all the time with the hdr/sdr slider in windows display props at 40%. In the Nvidia control panel set preferred refresh rate to max or you get stutter. Make sure the windows advanced settings and Nvidia refresh rates are the same or similar, i.e. 119/120 - 59/60.
In game including FH5 set the max HDR brightness to 800 as it's what an LG OLED realistically tops out at. Leave the other game brightness settings alone unless the defaults aren't working for you.
FH5 has more realistic lighting than FH4. FH4 had black nights and lights that popped. In FH5 it doesn't get properly dark but when the ducks line up it looks amazing.