A "public ledger" does not require a blockchain. There can only be one secure and permissionless blockchain, the one with the most hashpower and energy expended ensuring its security.

The most secure witness timestamp is the one performed on Bitcoin, because it is the most power-full time gain, and therefore ALL "public ledgers" that are not Bitcoin can simply be timestamped with Bitcoin OTS and the records published on something like nostr. This is all that is required to provide a public proof of ownership assignment for things like securities, real property and other non-monetary records.