I am sure, I have seen the GAFOR routes in an earlier version or on the trial.
Nevertheless, I actually don't see GAFOR routes with the "OMX" indications in Austria or Switzerland.
I have the latest version (3.6?)

At least in Switzerland I can see small, grey dotted lines where I usually find the GAFOR routes
Can I switch them on ?

You said the reference altitude is the lowest altitude it's safe to fly along the route. From memory that is incorrect; the reference altitude is actually the highest terrain along the route. If you flew it at that altitude, there's a good chance you'd fly into terrain.

@Tim: You'r right: the reference altitude is the highest terrain along the route, including obstacles.