Does he?
I don't know much about contracts but I'm assuming if he holds out he gets zero dollars, has no access to facilities, and is basically in limbo until he signs. Enjoy the CFL at a fraction of the salary, during which time MN will continue to hold your rights so you won't be able to play in the NFL at any point.
If I'm MN I'll wait him out and let Darnold take the snaps. It's not like Minnesota is contending for a championship, and they are likely finishing last in the division regardless of who is under center.