In my niche, bioinformatics, linkedin has become somewhat of a force ever since many people left Twitter/X during the 'rebranding'? It's quite weird.
They're mostly posts announcing new packages etc. but there seems to be more bioinformatics-y activity than, say, mastodon or bluesky. The posts definitely have a different tone than what OP decries.
Yes there are a bunch of weird niches that got a lot of Twitter traffic but found a home on LinkedIn when there's an overlap with professions. Another niche example that I see is applications for AI powered architectural visualization, many folks posting actually useful stuff there on a regular basis.
Honestly I wish people stuck with good old forums. There's forums for everything out there, in every niche, gaming, modding, hardware, cars, boats.
Every single community you can think of has likely a great forum out there, easily readable and searchable, where discussions on single topics last _years_ and go in extreme informative depth, the kind of depth that no platform like HN/Lobsters/LinkedIn can ever dream of.
The closest surrogate we have are issue trackers (like GitHub) or mailing lists, but even those offer such a poor UX that I can't but wonder..
The difference to linkedin is that biostars has 'in-domain experts' only; the postdocs, the staff bioinformaticians, etc. those are not the people who will hire you. The people who will hire you are on linkedin.
They're mostly posts announcing new packages etc. but there seems to be more bioinformatics-y activity than, say, mastodon or bluesky. The posts definitely have a different tone than what OP decries.