Follow up of T7128.
In the upper part of the certificate details window there is a line starting with "Private Key:" just above the tabs.
The info here is misleading if not all subkeys are stored in the same location.
See e.g. the picture below, where the primary key was moved to a smart card and deleted on disk, but the subkey is still on disk:
It seems only the storage location of the primary key is taken into account.
Edit 2025-03-20: We decided to leave off the "Private key" line with location info for OpenPGP Keys. The location can be found in the subkey details.
But for S/MIME keys we keep the line, as those do not have subkey information like the OpenPGP ones.