Ok the import might work, however in 1.4rc5 the preview3D view is bugged only showing me an occasional flickering triangle of the material.. (Win 11, RX 6600 XT)
This is a bug in AMD drivers which has been fixed in Adrenalin 25.9.2. Update your graphics drivers to the latest version.
If you still run into the issue, you could force Material Maker to run on Direct3D 12 using the --rendering-driver d3d12 command line argument, but this isn't guaranteed to work as I don't think Material Maker has been tested with it.