Can you add Cardano to MetaMask?
Cardano uses a UTXO model and cannot be added to MetaMask as a custom network.
Why it does not work
Cardano addresses (addr1…) and its extended UTXO accounting have nothing in common with the Ethereum account model MetaMask implements.
Search results promising a “Cardano RPC for MetaMask” are either describing a bridged wrapper token on an EVM chain, or they are simply wrong. There is no setting to change.
What to use instead
If you already sent funds to the wrong address
Funds sent across incompatible networks are generally unrecoverable, because no one holds the key to that address on that chain. The one exception is a deposit to an exchange: exchanges sometimes recover wrong-network deposits for a fee, so open a support ticket with the transaction hash before doing anything else. Anyone who contacts you offering to “recover” it for an upfront payment is running a scam.