Polkadot blockchain is not an EVM-compatible network and is currently not supported in MetaMask. We are hoping to support Polkadot in the future through our Snaps plugin system.
For more information from Polkadot, see here: https://support.polkadot.network/support/solutions/articles/65000168660-can-i-send-dot-to-metamask-or-mycrypto-wallet-
