Django releases time based and a version 3.3. was part of the plan. 4.0 is released right now because it is December 2021. The versions after that will be 4.1, 4.2, 5.0, 5.1 etc. [0] It's different from how many other projects work but not unique, Ubuntu works in a similar way for example.

And although it might be different form what you're used to, I really like it. If you check their documentation, you can see exactly when they'll make breaking changes and features will be deprecated and removed.

[0] https://www.djangoproject.com/download/