I have 10 bit support from Quadro Nvidia GPU and EIZO CG 279X wide gamut monitor with 10 bit support per channel.
I can get X11 to support 30 bits, but not the Linux aplications: GIMP, RawTherapee and Darktable.
30 bit support on linux Gnome is lost somewhere between X11 and final render in program. I suspect but do not know this is due to GNOME/GTK/Cairo. @hanatos suspect Cairo.
I am on Debian 11 with Gnome GTK3. GTK4 unknown to me
Gnome and GIMP and 10 bit
GIMP dev mail list:
https://www.mail-archive.com/gimp-developer-list@gnome.org/msg09813.html
I have not tested recently, so my feedback is a bit dated.
It seems one need vulcan or windows/osx/photoshop to get 10 bit per channel to work.