@Gargron I dunno if it's a workable concept, but old BBS systems back in the 90s usually had a bit of a "get to know you" questionnaire - and the workflow was usually that you could then log in, look around, maybe access one or two local message boards until you were approved for later access.
So maybe a "provisional" access step, so you're not bouncing completely - you can log in, maybe read-only, local timeline only? Instance-set options for access ranging from nothing to limited interaction?
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