If I remember correctly there was no output in console or log file, apart from the starting bits.
In fact the freeze occurred as soon as I clicked on the GPU tab in Preferences, prior to any operation involving gpu calculations.
My motherboard doesn't have any integrated graphic card, and I dicovered that the freeze could have been caused by an intel package installed, using the utility clinfo, which froze retrieving informations.
So I tried uninstalling all intel opencl packages in my system (used only by Blender), and the freeze with clinfo and metashape disappeared.
Reinstalling Blender with its dependecies now causes no harm, so the root cause for the freeze should have been an old orphaned intel package.