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Ledger isn’t exactly a cold wallet, its a hardware wallet. It holds your keys so that no action you take on a machine can directly expose them (unless you type them in yourself, bad idea!).
Coins on a Ledger won’t be on an exchange. If by yield farming you mean trading between coins all day on Coinbase etc, then no a Ledger isn’t for you. A Ledger is how you hold the coins (and by coins i mean keys-to-coins as of course coins are never actually ‚on‘ the ledger) locally, and spend them safely without potentially exposing your keys via a software wallet.