How do you keep a repetitive routine from becoming boring

I usually switch it up before I get bored. Every few weeks, or so. If you wait until you get bored, it's hard to keep going

If you work at something for long enough it becomes habit and it doesn’t matter if it’s entertaining. Like brushing your teeth isn’t entertaining but you do it because it’s just something you always do. Also if it’s a bigger task with room for a little customization, try building a routine with time frames and broader meanings like instead of saying 5pm: 1 hour of Cardio, try [4:00-7:00pm] : 15min – 2 hours of Physical Activity. This gives a lot of room for creativity and wiggle room depending on motivation that day so you’re still doing your routine even if it’s just 15min of stretching.

For me when routines become routines, I don't think about them, I do them automatically, so because my brain is not that much involved, it can't even decide that the task is boring. During routines like drinking water, brushing teeth or having breakfast in the morning, my mind can think about something else.
With routines like meditation, workout, journaling, the thing is, they are not repetitive. They are as repetitive, as if the routine was "watching TV". Yes, technically you are doing the same thing, but if it is boring or not, depends entirely on what you are watching. So those you can keep interesting for yourself.

I bundle the parts of the routine I’m not excited about with a small reward I am excited about. Breakfast after exercise. New podcast while cleaning the kitchen.

By creating routines that are both practical (easy) and fun. For instance, my morning routine consists of drinking water, showering, making my bed, get ready for yoga, have a nice breakfast, get dressed, spent 25 minutes on priorities then (re)schedule the day. Each of these rituals is useful, they give a sense of care (and also give the opportunity to take care for yourself), and give a chance to explore. How they do that? Well the drinking is nice because I'm thirsty in the morning, it also makes sure I take my medicine and supplemental vitamins. Once in the bathroom I can nourish myself with my favourite shampoo/shower cream/lotion. Or just wash my face. Whatever I'm up to. Refreshed, I feel like making my bed (make it look nice), and I get ready for yoga. No yoga routine is the same. Not even if you do exactly the same. Here I can tune in with myself and explore, challenge and/or nourish myself. Also it keeps me healthy and strong. After yoga I'm ready for breakfast. A nice breakfast could be anything. Of course, most of the time it's just a slice of bread, but the name invites me to make something nice or at least enjoy the breakfast. Now I'm almost ready for the day, I dress myself and start Hu the 25 minutes priorities. Next I take a look at the day ahead. Reschedule if needed. The priorities being done and the day we'll scheduled, I don't have to worry about/throughout the day. In the evening and the next morning I look forward to this state. So I'll start the ritual again.

Let's take the morning routine, for instance. You cam change the glass or bottle of water or add a slice of lemon or herbs (like peppermint) to your water. You cam change what you eat for breakfast every week , even prepare it the night before. Changing your exercise routine (add/remove different workouts or changing the targeted area are two possibilities). You can also change your alarm sound, from music to birdsongs or even use apps that let you wake up with mindfulness meditation or breathing practices. It all depends on you and your personal preferences. But keep in mind the benefits of the routine instead of the routine itself. And celebrate every step of the way