What is UTXO?
Really OP

Well maybe you could just search it , you will get it ..
All I want is a wallet with Bitcoin and USDC... and the ability inside the wallet to switch between the two at will.
Bitcoin and USDC or any fiat pegged coin you like are different from each other and they all run on different blockchains maybe some may rely on another blockchain/multiple blockchains.
The feature you ask for can only occur as an exchange I.e you give to another person, a firm/company to get what you want in return.. so you want it then you can get some non-custodial wallet that support fiat pegged coins, most will use a third party for exchange ( which are likely untrusted) unlike the real Exchange wallet that does it internally.