It is not open source, because it does not meet the definition of open source.

I’ve noticed that some “mobility” startups are using Linux. E.g. companies working on electric or automated vehicles.

Turn based, or at least have a pause button (in single player).

Yes, but does that still count as “modern”?

How exactly would it “get stomped”, and by whom?

I think you mean Tactics Ogre. Although it’s a spinoff of another game called Ogre Battle.

BTW, there is a miniflux package in Debian testing / unstable: https://tracker.debian.org/pkg/miniflux