Export issue: switching the coding level from 4,2 to 5,1 leads to oversaturation

When I increase the coding settings from 4,2 to 5,1 - which is necessary to export UHD - the export seems to add HDR metadata that it otherwise doesn't do. When I watch it on my smartphone, the video is oversaturated. My PC displays it correctly and also the thumbnails on my phone are correct. Just the video is wrong. All else equal, 4,2 leads to a correct display.
So it seems I am forced to export HD.

The HDR10 checkbox is unchecked, export color space is Rec 709, NDR (Nits) is set to 100, Profile is High, I use hardware-encoding.

My system:
Intel(R) Core(TM) i9-14900K
64,0 GB RAM
RTX 4080
Windows 11 Enterprise (Windows Feature Experience Pack 1000.22700.1077.0)