Which exact version from Help>About might be a start.
Try Tools>Database Check, check all the boxes and "Check", see if that gets rid of, or reports, anything.
Select the "Unfix" icon, then right-click, Unfix All and right-click>Done in the background canvas, fixed objects can be stubborn to manipulate.
Check that Everything, including groups is enabled in the find filter, hover the mouse over the item and right-click, see if you get a "disband" to breakup the group, that might make the elements deletable. Hovering the mouse should get you a datatip for the object type, that could get you on the way to deleting it.
It might be possible that the "route" belongs to a symbol, try File>Export>Libraries, send the library parts to a new subdirectory and open the DRA files to see if the route is actually in the library part, rather than the board.