Indeed, looking at the github project, it's not been actively developed for quite a while now.
A newer fork does exist (but still not been touched in a few years)
https://github.com/Xyrio/RSSOwlnix
This seems to be a bit more up to date. I'm not near a linux machine to test it out though
If you dislike the Google Play store, then you might want to consider what the F-Droid has to offer, such as at https://search.f-droid.org/?q=rss&lang=en .
For example, do you have access to a webserver on which you can run Docker or LEMP? Then you might want to run Tiny Tiny RSS on that server, and TTRSS-Reader on your phone.
(I've become somewhat spoiled on my desktop by how well RSSOwlnix just works, and have yet to find a phone-based RSS reader that works as well.)