I have been flagging these posts individually, but I thought maybe a meta question would be a good follow-up, in case the moderators are not aware of the behaviour. As @YemonChoi points out, the author of the post Is renormalization a valid reason why the riemann hypothesis could be undecidable? has been creating many new accounts, which originally asked about a specific paper, but now appear to be moving on to general questions about the Riemann hypothesis. I don't think the questions themselves are valuable, as I described; but, setting that aside, surely the MO norm is not to allow a multitude of accounts for the same person.
What they're doing here on MathOverflow is relatively harmless. They're also active on other sites in the Stack Exchange network, where they are posting downright abusive stuff; here are some examples. That doesn't mean they're forbidden to participate here, but it speaks volumes.
Do note that sometimes users don't register themselves (because they don't want to or don't know the benefits); the system will remember them by the cookies in their browser but if those are cleared, they'll end up using a new account if they visit the site again. Or they might have forgot their credentials and simply signed up with a new account.