Never heard of any Web3 website that uses metamask with your ETH address(Privkey) to generate a Bitcoin address.
Are you sure that it is a Bitcoin address? Do you know the 3 first character of your Bitcoin address? Legacy/Bech32 address?

Why not export the private key of this Ethereum address from your Metamask wallet and import the private key to any Bitcoin wallet like Electrum?


Or you might be talking about Zion here's their website btc.justsnap.io