I often have the feeling that kids today lack the experience of being part of something.

Metal can provide this, especially live concerts and the fandom is pretty stable: You meet the same people again and again in your tiny very noisy social bubble.

The whole 6-7 or „chicken jerky“ madness felt very similar to classical group formation dynamics: Be part of it by knowing the secret rites and separate yourself from outsiders that don’t.

The sad thing about those TikTok movements as opposed to metal is: The feeling to belong is an illusion. There isn’t real group just a set of strangers that share a fleeting experience that rarely creates something lasting, a „one-night stand“ like experience if you will.

I think you've nailed it and it's kind of depressing in a way since there were a lot of things kids were part of just a few decades ago. The local football group, the bunch that gathered together to watch a TV show at one guys house that would air at 7:30 pm on a weekend, the circle of cousins kids would hang out with during a stretch of holidays, the circle of people who they'd meet regularly during a congregational prayers, etc. etc.

These things are as missing as they're necessary in kids' lives and (non-mainstream?) music gives people some semblance of community that has a stabilizing effect.

The Discord "communities" don't have the same effect unless the group actually meets in person regularly.