The last time I used Metamask, it is only supporting altcoins and not supporting bitcoin.
I do not want to download Metamask to check this which I think is a long process than asking on this forum.
That dapp will enable users to sell BTC directly for fiat via Visa card. they'll probably use Wrapped BTC for metamask. but transak itself works with multiple other wallets so it's likely to be possible to sell actual BTC too via Visa Master Card.