The exchange gets to take however much they want from you. For example the way dogecoin is transacted across the blockchain, like when you are sending dogecoin to an address from your wallet using dogecoin core, you'll only be paying about 0.002 doge as a fee to get the transaction added to the ledger.
An exchange is just an organisation that is not at all related to the functioning of the blockchain. an exchange will sell you cryptocurrency for money or other cryptocurrencies, and if you ask nicely, they might let you withdraw. something something about "not your wallet, not your coins"
I don't actually know how exchanges like to interface with the dogecoin network, whether with some sort of API or their own special sauce that they use to automatically handle wallets and transactions .
I've seen some charge as much as 20-50 dogecoin to withdraw, it's basically robbery.
Actual on chain transactions take 1 min to complete as dogecoin blocks are completed every minute. The fee is .0025 dogecoin.
I've had rounds with exchanges over this, the common thing seems to be that the initial levels of "support" know nothing, they just know what they are told or is in their SOP.
I once had a tx with crypto dot com take over 8 hours to come to my account. I spent an unhealthy amount of time arguing with a dozen of their support people who kept talking me in circles attempting to tell me it was network congestion. When I pushed back showing them there was no congestion they said it takes 50 confirmations, when I said those confirmations happen once per minute they went back to network congestion.
I put in way more effort then I should terracore attempting to get somewhere with the situation or get them to admit they were doing something manually on their end because of how long it was taking. But just got support speak over and over.