Any way to show old courses?

I'm not sure if this is as elegant as you're thinking, but you can set a course to "always display" (or similar language, I forget exactly) so that it will always be displayed on your map screen. No need to load that course or start that course when you ride, it will show up on the map screen regardless.  This is how I usually navigate MTB routes because I'm not interested in turn by turn or guidance prompts.  I just want to be able to glance at the map and see if my location is on the route or not.  

Go into whichever course you want shown and find the always display option for it.  Sorry I don't have my device with me to offer the menu steps.  You would have to go in and do this for each course you want shown unfortunately. I do believe you have options for changing the course color on the map as well.

Thank you so much for your reply and help.

What I would like to see are the rides already done (I don't know if the right word is route or course), not the routes/courses uploaded via Garmin Connect or Basecamp (or other app like Komoot).

I've found the "always display" only for route uploaded by me, not for the routes created during previous ride.
Surely I can download these and upload on the device view Connect or Basecamp, but if there is any way to do directly on the Edge 530 would be nice.

The only way to do it on the edge is to create a course from a previously recorded activity. Then use the always display option to display it on the map