I have always worked for product companies, on products that I find interesting. Currently it is a product for margin calls in finance, before it was SMS routing and delivery, before that VoIP. Even if everything I do isn't new or interesting, there is enough variations and challenges, both in the code and also learning more about the domain.
The times I have started to feel that it was boring and repetitive, I have changed jobs (but I've stayed at least 5 years in each place).
I also like to try to get better at what I do as a developer. Mostly this is by reading books or taking MOOC courses. I think there is quite a lot to learn about developing SW well (because it is a really complex activity). So that also keeps me interested.
About eight years ago I also started blogging [1] about SW development. I've found that trying to formulate what I think about it has also kept it interesting.
Thanks for sharing. I'm currently doing fullstack web development and find it not as interesting anymore as it used to be (close to 6 years now). I'm trying out various projects but it is either need higher learning curve such as deep Math (i.e., machine learning, graphics) or domain specific knowledge which I usually don't have expertise about.
I also like to try to get better at what I do as a developer. Mostly this is by reading books or taking MOOC courses. I think there is quite a lot to learn about developing SW well (because it is a really complex activity). So that also keeps me interested.
About eight years ago I also started blogging [1] about SW development. I've found that trying to formulate what I think about it has also kept it interesting.
[1] https://henrikwarne.com/