Anytype is local/offline first, P2P, end to end encrypted, open source, and has a great mobile app. They provide a (storage limited) cloud backup peer for free. You can either self host that yourself, or just rely on P2P syncing with your other devices. I’ve been using it for years and really like it.

https://anytype.io/

Anything done by Michel Gondry, but this is a favorite: https://youtu.be/gLESpHrtvxs?si=zdeITwz-fe29LJlU

I just can’t imagine how much time was spent making that.

Everyone should know that, very often, they are just wrong. And that’s ok. We all are.

The more ready you are to really accept that you could be wrong about anything, and admit when you are wrong about something, the better you will make your own life, as well as the lives of those around you.

Tubthumping

It all still works great for me across all my devices (Linux, Synology NAS, Mac, and iOS) plus it looks like their community forums are still active, and they have packages for Synology DSM 7, which is relatively new. The last iOS app update was 2022, but maybe that’s just a sign that it is stable and doesn’t need frequent updates?

I wonder if you were using their old software called BitTorrent Sync. At some point they did a rebranding, and it could have left you with an abandoned client that stopped working, maybe? ¯_(ツ)_/¯

Bummer that it’s not working for you. It’s definitely one of my favorite apps.

Resilio Sync is fully cross-platform P2P app for syncing files/folders: https://www.resilio.com/individuals/

I’ve been using it for years and love it.

Edit: Sorry, it’s not FOSS. My bad for not reading the question thoroughly.