It is mostly local operators rather than the big international chains you see at every airport in Western Europe, but honestly that works in your favour because the prices are way lower and the owners are usually pretty flexible with pick-up times. Roads between Skopje and Ohrid are decent, though some mountain passes get a bit narrow and winding, nothing too crazy but you want something with a bit of power for the climbs. Sorting out a rent al car in North Macedonia before you arrive is smarter than rocking up and hoping for the best, you can see what is available here
https://getrentacar.com/en-US/north-macedonia .