We've been building a lot of content systems lately and found Wagtail to be pretty useful (https://wagtail.io/). We build pretty much everything on Django so it's a natural fit for us.

Understanding the models and the way they show up in the admin takes a bit but it's pretty smooth after that, and very programmable. And its built-in API uses DRF, so you can expand on it with that easily. Our frontends are all React-based and it works out very nicely.

Looking at this I kind of checked out once I saw Java, which I'm not inclined to deal with these days. To each their own of course.