The app is discontinued.
Now that the Android app “syncthing-android” has been publicly archived, we still have with Catfriends fork version for individual installations, which works also since a long time reliable.
However, I had always installed both apps for internal synchronizations, which worked smoothly if a few port rules were followed. Now that I no longer have the archieved APP, I would have to install the fork version twice, but the question is how to do that.
You can do this through the work profile (see https://support.google.com/work/android/answer/6191949), but then each instance will only be able to access files from their respected profile, which may be a significant limitation.
Otherwise, I cannot think of any other way than cloning the app. This is completely unsupported and not really “allowed” by Google, but I’ve personally used https://appcloner.app for this purpose. However, please keep in mind that this is a 3rd party app that is 100% proprietary, so you will be installing it at your own risk. There may be others, but I haven’t been able to find an open source alternative.
On a side note, even without future updates, the official app will still likely continue to work as expected for years to come.