0.0045 ETH in a “Trust” wallet. The course taught the value of a cold wallet to hold assets “off-chain.” But I understand my funds listed above are “hot.”

My goal is to do DeFi lending and/or a liquidity pool.
Do I have it correct that while my assets are in use in DeFi they could not be in a “cold” wallet?

Would you recommend a wallet(s) better suited for DeFi ? (e.g., Lex mentioned MetaMask)

Correct. And MetaMask is the go-to for many re DeFi. This is not advice.