You're wrong.
Yes, Starlink won't work because of the 3G sunset. (Cell phone companies stopped using 3G, it wasn't a "Starlink 3G network" that went down.) Unless, as @Accustiver mentioned above, you got the upgrade to 4G done, which Subaru offered for free for a while if you were a Starlink subscriber. Depending on your car's hardware, that upgrade may have just been a firmware update, but it could have also required a hardware replacement. Apparently the Starlink module is separate from the head unit, and some of them had 4G capability, though it wasn't enabled. I believe they still offer the upgrade, but it's quite expensive.
As for the Starlink app, Subaru has discontinued it, but I think the My Subaru app has replaced it. As far as what it may be capable of performing on your car, if you upgrade Starlink, I have no idea.
Navigation updates are handled by a third party. ( https://here.navigation.com/models/Catalog/Catalog_Subaru/en_US/HERENA/USD ) The latest maps are over a year old now.