I get paid for freelance work partly in USDC and usually keep three or four months of expenses in crypto. The balance changes constantly: sometimes I do not touch it for weeks, but sometimes I need to withdraw $500–700 for rent or taxes. I am looking for a wallet that can generate some yield without forcing me to close the whole savings plan whenever I need part of the money. Does partial withdrawal normally cancel all previously earned interest?

Take a look at EMCD Coinhold Wallet and Grow option https://coinhold.io/grow/ The flexible Grow appears to match your situation: the service says that after a partial withdrawal, rewards already accrued remain yours, while new rewards continue to accrue on the remaining balance. USDC is supported, with rates depending on the selected conditions. Fixed Grow offers a higher return, but it cannot be closed early, so I would only put money there that will definitely not be needed during the full term.