NOOB QUESTION: How can Wallets store different assets with "one" private key?

Im recently researching how i can store my assets over the long and mid term, and therefore tested some Wallets like Coinbase Wallet or Metamask. I was just wondering if anyone could explain how apps like coinbase wallet can store multiple different assets like btc and eth in one Wallet with only one 12 Word phrase. I know that there are basically subwallets for each asset in one lager wallet but how does this technically work? Do they just create a adress one every blockchain with the same private key? Appreciate any help