Hello @jhmnieuwenhuis. I see something similar on my side, on Linux Debian.
If I build regular RT dev branch then the selected output color profile in RT editor is respected when I push out, to GIMP, in my case and GIMP opens and displays the file with my chosen color profile .
When I use my experimental fork and branch metadata-exiv2-update this is not the case. GIMP starts and the picture is displayed in GIMP, but with GIMP default internal sRGB profile.
This is not correct. The output color profile selected in RT should be respected when pushing out to external application.
I see the same thing (chosen RT output color profile not respected) even in branch metadata-exiv2, from RT main repo, before me merging in dev in my own fork and metadata-exiv2-update branch. => I think, but I do not know, that this is not due to the many merge conflict resolutions I had to make. The root cause is in the old code in metadata-exiv2, from RT main repo.
However I need to do more testing and check the settings of my GIMP application.