The fossify apps are legit, I use them daily.
This is the same or similar situation as OpenOffice → LibreOffice or OwnCloud → NextCloud (and to a lesser extent but more similar scenario, Audacity → Tenacity or various other forks).
This is what true open source looks like in action.
Meshcore also has a paid license to use the full feature set and if Plex has taught us anything, it’s to stay away from garbage like that. I’ll stick to Meshtastic, thank you.