Boring exercise is worse than bad exercise.
As beneficial as it is to have a regular exercise routine, sooner or later you’re going to get tired of it. Familiarity breeds contempt, as they say. If you keep going even if it’s boring, you’re just going to get tired of it. Before that happens, you need to mix things up a bit.
If you feel you’ve hit a plateau, the first and most obvious solution is to up the difficulty. Add more reps to your set, or incorporate challenging new moves. You can create interesting new compound exercises by combining the movements from two different exercises. Two benefits from one set! Look around online for viable combinations. Be careful about combining stuff at random, though; some moves don’t mesh in healthy ways.
Try incorporating exercise into your other interests. If you enjoy listening to music, for example, try assembling different playlists for different exercise sets. Or better yet, do it the other way around; try to determine what kinds of exercises go best with certain kinds of music. It’s kind of like an open-ended puzzle; it’s fun! Alternatively, put yourself into physically strenuous situations. Take long hikes and snap lots of pictures. Jog around your neighborhood and greet your neighbors. Join a fun run!
If adding to what you already have isn’t doing it for you, then the answer is something new. Try a form of exercise you wouldn’t normally do. You can start small by just adding some new moves to your set you haven’t tried before, or you can try a brand new activity altogether. This could be something like tai chi, shadow boxing, or step aerobics. Maybe you never wanted to try this stuff before, but if you want something new, then you gotta step outside your comfort zone!