I recently became aware of the fact that exchanges have trading engines that execute all trades within the exchange itself, and not on the blockchains. That is to say, if User A sells to User B, there is no corresponding blockchain transaction transferring those coins. Instead, both users have accounts on the exchange which are debited and credited. A blockchain transfer only takes place during deposits and withdrawals.
Please explain the same case for currency like Bitcoin as it manages its assets using UTXO Model which is a record of unspent outputs. And for other currency like Ethereum using the account-balance model as the transactions aren't included in the blockchain. So, how they will reflect changes in the account of a user?