how exchanges like binance or kucoin storing user assets

my question are listed below i would be glad if anyone could help im stuck a little bit

  1. an exchange creates unique deposit addresses for each users . are theses addresses all derived from a HD wallet and exchange controls all the keys and indexes ?
  2. if the above answer is yes then imagine exchange need to collect all funds periodically from hot HD wallet to a cold wallet . do they iterate over each wallet address index and transfer funds using that index private key for each user address and pays a fee each time or there is something i missed ?

3.imagine cardano wallet which generate new addresses for each transaction can this be done for all blockchains plus using hdwallet features

  1. and can i use only hdwallet master private key and move all funds and pay fee just one for moving all fund from diffrent addresses

Thankyou!!!

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