Noob Questions about “Malicious Smart Contracts”

I'm relatively new to crypto so pardon any misuse of terms. I've read instances of people who purchased and/or interacted with coins that had malicious 'smart contracts' embedded which essentially made it possible to drain funds from their wallet at a later point. I'm transferring crypto that was purchased on a well-known exchange to a cold wallet. The coin is MANA (Decentraland) which is on the Ethereum blockchain. Should I be concerned about depositing this coin in the same wallet as other assets (BTC, ETH, etc.)? I

I wasn't sure how these alleged smart contracts work–is it possible for the the smart contract to be embedded in one coin (i.e. MANA) but drain other crypto currencies in the same wallet?

Is this primarily only a concern when purchasing from sketchy/lesser-known exchanges?

If I were to have one of these malicious smart contracts in my wallet, would isolating the affected coin to its own passphrase wallet protect the other coins in the main wallet? Thank you.