I don't have a clear path for you, but my feeling is that you might already have developed a taste for systems programming, and Java backend development is not

I don't have a clear path for you, but my feeling is that you might already have developed a taste for systems programming, and Java backend development is not going to keep you happy. Of course I could be totally wrong, but it sounds a little bit like you care about being close to the metal and the challenges it presents, while most "Java backend" jobs will keep you working on a very high level, often programming CRUD apps and other "business logic" that may be interesting from a business perspective, but not necessarily from a programming one. Definitely a good idea to try writing an emulator, though. Writing a Game Boy emulator is popular: It's just at the right intersection to be a simple enough architecture to get results very quickly, but with enough intricacies if you dive deeper to keep it interesting.