I understand that but when I move a file into separate encrypted volume created by an app like Crypto disks which creates a volume like in Veracrypt, then in this instance I don’t delete a file but simply move it into that encrypted container. So by this logic the file I moved cannot be retrieved, is that correct?
That is not correct for this reason:
When you are moving files between volumes (or containers), it’s actually a copy, check and erase operation. Otherwise, any disruption could lead to the loss of the file.
This said, it’s not very risky on iPadOS, because the storage is always encrypted. You would need access to the operating system to decrypt the storage (or guess the drive’s decryption key, which is not 6-digit long
but is locked by your passcode).
If you are worried about the information stored on your iPad’s internal storage, make sure you have remote erase capabilities (e.g. Find My), as that will blow away the device’s decryption key, making data retrieval extremely difficult. The people that would be able to get to that information will have very advanced means (e.g. state actors) or be very dedicated (many years/decades). Caveat: a defect in the software might be found that makes it much easier, but so far, it has been rock solid.