Dark Video/Gama Shift from Davinci Resolve to YouTube
The MOV you exported from Resolve is tagged as Rec 601 (despite being UHD).

So, I transcoded your MOV using the command below, preserving all color characteristics and uploaded that to Youtube. Downloaded YT's transcoded video and compared it to the MOV, and in ffplay, VLC or Potplayer, they look the same.

ffmpeg -i Untitled.mov -crf 18
       -color_primaries 6 -color_trc 6 -colorspace 6 -color_range 1 resolve-upload.mp4


P.S. I also uploaded your MOV and downloaded its transcode from YT. Turns out that the transcode is flagged as Rec. 709, which is wrong, despite the MOV being tagged as 601. The rip of my transcode is tagged as 601.