Preferences Color Management Policies
Running GIMP 2.10.10 on Windows 7 Pro 64-bit, Color Management Policies File Open Behaviour does not seem to work. I am editing TIFF files created from scanned color negatives. File open behaviour is set to "Convert to preferred RGB color profile." The preferred profile is set to ProPhoto RGB.
When a TIFF file is opened in GIMP, its Image Properties say, "GIMP built-in sRGB" on the Color Profile tab.