The emulator was actually announced in a YouTube video back in 2019, which means that it took the developer about 2 years or so to finally release it to the public. It isn’t the only emulator because as Kotaku notes, there are several others, but none of them save for Spine are ready for public consumption yet.
However, it should be noted that while Spine can run PS4 games, it might not be able to handle everything thrown at it, especially triple A titles. Instead, it seems like this is more of an emulator for indie-based games that aren’t quite as intensive, so if you were hoping to be able to replay some triple A PS4 titles, think again.
Also, do keep in mind that Spine is purely an emulator. What this means is that it’s just the platform you use to play games, and that if you want to look for the ROMs of the games you want to play, you’re on your own.