Sounds like it's basically dead. The issue with messenger apps is that they're a dime a dozen, there are so many of them and they offer so much variability in security, privacy, but most importantly usability and uptime. If your friends won't switch to them, there's almost no point in having them or using them.
Briar was unique in its ability to discover peers over local networks and Bluetooth - Very few if any other messaging apps do that.
Unfortunately the security/usability tradeoffs mean it never was going to hit Whatsapp levels of use, but it certainly fills an important niche.
For most IMs I agree, Briar is/was slightly different though, being P2P and E2E encrypted. There isn't many IMs out there supporting Bluetooth connections between users for example.