I found no easy and clear tutorial for getting a 4K video out of my Panasonic GX80 / GX85 to record this in HQ. So I connected an Atomos Field Recorder with the GX80 HDMI and made this workaround.

First, go to Motion Picture / Rec Format. Set the Rec Format to MP4.Go next to Rec Quality.Set 4K 25p or 4K 24p.Go next to TV Connection. Set off the HDMI Info Display (Rec). Here is the result at the OSD of the Atomos: 4K 25p

To use the DMC GX 80 / 85 as a video camera I had to do some customisations. Have a look at this post https://mind.work/2019/05/24/customized-pansonic-lumix-dmc-gx80-gx85/