the transaction is first order, the UTXO is second order

the process of verifying a transaction on bitcoin is walking the web of UTXOs from a current one, tracing the path back to all of the coinbases of all of the inputs, coinbases are the minting of a coin, the block reward

the UTXO is an abstract concept made from this tracing operation to verify every sat in the utxo is rooted in a coinbase and thus has not changed the supply outside the consensus parameters (which can be, in fact, *at the time of the block height the counbase was created in)