Withdraw USDC with USD balance

My ultimate goal is to transfer USDC from Coinbase to my own wallet. On Coinbase I can’t create an order for USDC because the product USDC-USD doesn’t exist. I understand that this is because USD and USDC are unified. However, when I try to withdraw USDC using Coinbase Cloud I get the response “insuficient funds”. When I set the currency to USD I get “network doesn’t exist” with network set to “ethereum”. Any help would be appreciated!

Also, slightly related, is there a way to get the supported networks for a cryptocurrency through the API?