I have found both iOS (iPhone) and iPad OS to be limited when transferring from a card reader to an SSD via either an iPhone or iPad Pro using an external dock due to the inherent file handling limitations in both these OS's. Fine for a few RAW files but choke when trying to transfer a couple of hundred GB of RAW files.
In my case in total frustration I set up an appointment at the Genius Bar in the local Apple Store, took my iPad Pro (M2), OWC Thunderbolt 4 port dock, Sandisk SSD, card reader and Delkin Black CFe Type B card containing about 210 GB of files, etc., etc., hoping to find a solution to my problem but the Apple expert with whom I was dealing eventually gave up in frustration.
I ended up buying a 14" M2 MacBook Pro for the overseas trip I'm currently on. Ouch - a relatively high $$$ solution!! But it is painless, very fast and works flawlessly.