No Syncthing is perfect. The problem is the Android app development issue. The main all had it last update ever earlier this month.

Presuming the software is working ans secure, is the time that passed since the last commit importang?

Maybe but openvpn is a complex beast with a huge attack surface. Wireguard is beautiful, minimal and even in your use cases no real problem to setup?

Why? Wireguard i a great protocol and Mullvad best in class with regards to privacy.