ffmpeg: How can I convert from H.265 into another 10bit format for colour grading?
I'm not familiar with DaVinci Resolve, but if the free version supports 10-bit H.264 you can use HandBrake to transcode to that format with CRF 0 and see if that works.

If that doesn't work you'll need to use FFmpeg. With a bit of fiddling I was able to convert your source file to DNxHR using this command:

ffmpeg -i DSCF1265.MOV -c:v dnxhd -profile:v dnxhr_hqx -color_range 2 -c:a copy DSCF1265.dnxhr_hqx.mov

This also copies the audio over, if you want to exclude it for some reason use -an instead of -c:a copy.

The -color_range 2 bit is important, without it the output looked different from the input (at least when watched with mpv).