Just in case someone else ends up here from a google search, I can verify that this behavior of being limited to 5 workspaces is still a problem. However, @AntiqueAntelope 's fix of digging into the settings, finding the sidebar player toggle and flipping it will solve your problem.
Specifically, here are the steps:
- Open your preferences
- Search for "Enable Player"
- This should pull up only the toggle you need.
- Switch it "OFF"!
4.5 IF the toggle is already off, toggle it "ON" and then "OFF" again! - Add a new workspace and it should appear and stick like it should.
Fixed!