That is it bud. So old wallets cannot be used? It costs to transfer funds to a new wallet. Transfer fees.
As the warning says, old wallets can be migrated (i.e. upgraded) to the descriptor wallet format using the utility built into Bitcoin Core. This process only modifies the wallet file on disk and does not cause any transactions. There are no fees in order to migrate. The migration tool will exist in Bitcoin Core for a very long time, if not forever.