For now it looks like the original developer of the fork [0] decided to retire their efforts including their whole GitHub account.
User nel0x [1] is communicating with the new repo owner.
https://github.com/researchxxl/syncthing-android/issues/16
>> Hi @researchxxl, I initially thought this might be Catfriend1’s new account, but apparently that’s not the case.
>> That's one of the biggest challenges I think for getting started. It's not about if we are allowed to, but if you don't already have Catfriends1 key, we probably won't have any way of obtaining it :/
>> i got the key when the repo was transferred to me.
>> Catfriend was on the lookout for a successor and I already knew him from another OSS project they did a while ago. we agreed and I was asked to create a new account after I got keys and creds to their original account. it turned out to be a bad idea to reuse their name so I created a new one.
[0] https://github.com/Catfriend1/
[1] https://forum.syncthing.net/t/does-anyone-know-why-syncthing...