I don't understand why as a developer I'd want to use LinkedIn. I have StackOverflow and GitHub which a lot of relevant leads come from. When I buy a used car - I don't publish a "I'm looking for a used car" post and wait for car salespeople to approach me. I go and charactarize what I'm looking for and then go car-shopping. When I look for a job - I don't publish a "I'm looking for a job". Talking to the recruiters…
I completely agree and I do both of those. I used to do a lot more in open source, but had other life priorities take over. Meeting and talking to engineers, though, I liked that so much that I ran a physical space dedicated to it, and will likely do something like it again.
(Aside: The rapid shift to online meetups has been great lately - I've been to a number of meetings and even conferences with fellow engineers in countries I would not have realistically travelled to.)
However in my experience, and I know it's not the same for everyone, "contributing to open source and meeting and talking to engineers and building things", fun and rewarding as it is, has not tended to be a good route to paid work. If anything it's been a significant net expense!
The point of my comment is that, unfortunately, even for developers the "fun" approach doesn't work out everywhere.