FranceBB, Thanks for your post.
Here's "new" HLG file 20190831-160457_RTL UHD.mkv (135MB)
https://yadi.sk/i/SRloXWrOP-L-xA - mpv.exe plays it with right colors and and mpv.conf with "--hwdec=auto" near it to play with hardware acceleration if it's supported by videocard.