Briar requires manual pairing between bluetooth devices.

Maybe taking a look on

geogram

When the internet goes down, Geogram keeps going. Direct device-to-device communication without servers, accounts, or infrastructure you don

? Each phone becomes a station/server if desired and you can confortably exchange BLE messages/pics with anyone around. To exchange large files you can plug a USB-C cable between both phones. In addition to that is supported LAN, Internet and radio messages (APRS). Sneakernet is possible but not yet implemented. Feedback and testing is welcome, NOSTR is native.