Seems like it will be around for some time, based on the developers comments

Hi, Syncthing-Fork is a personal project, originally meant to keep the Android app alive for my friends and family. I’ve shared this work from the very beginning and will do so when I hit the code for updates. I will primarily do compatibility with the Android phones “we” use here, so that’s currently the range from Android 10 to 14. Feature development is currently not on my roadmap. I myself use the app and depend on the availability of Syncthing on the Android platform for my own workflows. You’re welcome to use the releases on F-Droid or my GitHub if you like the fork. Kind regards, Catfriend1

Per GitHub

Afaik you need some external resource to coordinate the punch. The STUN protocol is purpose built for this, and both clients need to be able to reach a STUN server to coordinate which port and public IP they’ll try to connect to each other on. I assume this does something similar but with p2p network tech instead of a STUN server.