Most blockchains have a RPC API set which allows to read content of blocks , find details on transactions and find assets - coins/tokens held by a specific address.
This way allows finding total number of addresses on the blockchain, assets of each address, and transactions by each address.
However there is no public information which shows the identity of a person holding one or more addresses.
Only some government agencies can force wallet providers and centralized exchanges to disclose individual identities and their crypto addresses and assets.