Hi again Tenoch,
The Puppy Package Manager for fossa 64 has Qt5 version 5.12.8, not anything newer. I'm not sure where you got OBS from. If it was built by someone on the forums, it might be built against a version of Linux that is not fossa 64. Their OS might have Qt5 at 5.15. There are some ways you can download and install 5.15, and possibly other libraries, into fossa 64, but that can be a headache (as pointed out by norgo and mikeslr). The better solution is to get OBS that was built for fossa 64. That way all of OBS' dependencies, such as Qt5 5.12 will be set up correctly.