If you go to the OBS Installation page [1], they list a number of repositories for various distros. They seem to maintain their own for Ubuntu, which appears to contain the latest version and the repository for openSUSE Tumbleweed does as well, although it does not appear to be maintained by the OBS Project.
If you refer to the features described here, they might not be in any release yet and you might need to build from source.
Installing a bunch a different repositories for every new version of a software you want is a risky recipe to get a system that will break something on upgrade or that you get barred from upgrade because of some packages or can't upgrade some packages... things like these.
On the other hand, even with ubuntu 16.04 (supported until recently) you can easily get the latest version through flatpak.
I don't personally take issue with Flatpak (though I don't really like Snap), in fact I would likely publish my own applications as Flatpak if I needed to, I just wanted to answer the question of the grand parent.
I can't really speak for the Ubuntu PPA, but the openSUSE repository is the big third party software repository that almost everyone uses anyway. I'm not sure if it's quite accurate to call it the equivalent of the AUR, but it should be similarly widespread.
Project you want needs libA>2, your system provides libA=2. For reasons unrelated to the system itself they can't be installed together as proper packages. PPA may be able to solve it with vendoring, but it's a pain and distro-specific. Flatpak does not have this issue by design.
If you refer to the features described here, they might not be in any release yet and you might need to build from source.
[1] https://obsproject.com/wiki/install-instructions#linux