You must learn a basic, people can create and use as many Bitcoin addresses as they want. They can do it easily with a good open source non custodial Bitcoin wallet software.

What you tried to find is impossible and only tips of iceberg. Like you can not find any on-chain analytic tools or parametric that can give you how many people own bitcoin so far. They only are able to give you total number of Bitcoin addresses that have bitcoin.

Forum admins, moderators have their Bitcoin addresses on their profiles to get donations or salary.

Many Bitcoin developers have their donation addresses at https://bitcoindevlist.com/ (Bitcoin Donation Portal) but you can not know how many bitcoin each developer has.