Globally, Spring Boot is more demanded than Django. For example, there are about ten times more open positions for Spring Boot than for Django in Brussels. So this naturally drives up the price of developers mastering Spring Boot. If you have an opportunity to work with Spring Boot, I suggest you take it, as it is a sound career decision. Furthermore, your experience with Django will help you to master Spring Boot, as both frameworks share many concepts. That said, Django positions do also exist, and it's absolutely not a bad decision to become an expert with that framework either. Django developers seem to like it very much.

My mantra is not sticking to a particular technology. That is what I'd suggest. Going by that, I recommend you learn both, Django and Spring Boot. But if you want to choose one among the two, I'd say stick with Django. Saves you the effort of learning a new language and a new framework. Rather, you can spend that time honing your Django skills. It is a wrong notion among young graduates that organizations decide pay based on your technology stack. You just need to be good at a technology that is in demand. You'd be paid well no matter the technology. Django is a wonderful framework and there are tons of companies looking for Django experts. The same can be said about Spring Boot. Both are wonderful technologies in their own accord. As for you, just go with the technology you are already familiar with. It is a misconception that Spring Boot developers get paid better than Django developers.