FWIW not only is the project alive (last commit 17 hours ago) but distribution too (cf links above) and project management too (cf e.g. https://github.com/orgs/LMMS/projects/1 as example of complex set of tasks mostly done toward a major release).
So... I'm not going to give people working on LMMS any advice, but of course I hear you, and OP, when it shows for people who aren't deep into it a project that seems abandoned.
I do not know no why the project is in that state but what I hope I have shown is that for sure it's very much active.
Happened to me with another brand and model (can't recall which to be honest). It did pair but appeared as a generic BT device, not headphones, and thus was totally useless.
I was pissed.
Then... I pair with something else, not a computer but something simpler, maybe a phone, I can't remember, and it worked. So I was shocked, how can for this it works, clearly no driver installed on top and not my desktop?!
Anyway long story short I tried again few more times and it worked. Headphones were now pairing as headphones.
I can't explain why but my point is, I wouldn't give up. I would retry to pair few times (I know, sounds ridiculous, and yet...) without changing anything.
PS: if you know the ins and outs of the BT stack and it makes sense to you, please do explain! I'd love to learn