I need a messenger app that is working for over 100 meters without internet and i want it to be as stable as possible.
Briar | F-Droid - Free and Open Source Android App Repository maybe? Has BT but not multihop (yet afaik)
Briar doesn’t need additional Hardware. Imho Wifi has a longer range than Bluetooth. Can you use an additional Wifi Hotspot or maybe special antennas?
is in the IzzyOnDroid Repo, needs additional hardware and has a CC-BY-NC-SA licence. See also: GitHub - markqvist/LXMF: Lightweight Extensible Message Format for Reticulum