See GIMP - GIMP 2.10 Release Notes
“High bit depth support allows processing images with up to 32-bit per color channel precision and open/export PSD, TIFF, PNG, EXR, and RGBE files in their native fidelity. Additionally, FITS images can be opened with up to 64-bit per channel precision.”
I just imported a 16-bit grayscale Photoshop file and GIMP retained the embedded 16-bit Adobe Gamma 2.2 Grayscale profile.
I haven’t tested more than that.
Is GIMP now a valid alternative to Photoshop ?