Re: Anker 735 GaNPrime 65W - wrong choice for IPadPro + Sandisk SSD?
Are you by chance using NTFS on the external drives?
A lot of external drives come formatted using NTFS. macOS can read NTFS volumes, although it needs help from third-party drivers to write to them. I don't believe that iPadOS has any NTFS support. (Until fairly recently, it would have been dead weight.)
Apple Support – Connect external storage devices to iPad says that
"A USB drive must have only a single data partition, and it must be formatted as FAT, FAT32, exFAT (FAT64), or APFS. To change the formatting of a USB drive, use a Mac or PC."
Mac OS X Extended (Journaled) (HFS+) format isn't in Apple's list. (An iPad running a recent version of iPadOS would always use APFS for internal flash storage.) But one Apple Support Community discussion thread claimed that iPads can read and write HFS+ volumes. I haven't tested that one way or the other.
Most of my external drives are formatted Mac OS X Extended (Journaled), a few APFS, some FAT32 and some exFAT. The fatties are not password protected and indeed they work with the Ankers - thank you for getting me there! One of the APFS volumes is a Sandisk iXpand and that one works too (like it always did, of course). The other APFS one is a password protected HDD that does't show up on the IPP. The Sandisk SSD is formatted exFAT, so in that respect it should work, but it too is password protected and the iPad doesn't "see" it. So I guess password protection is a no-no with this configuration?
At the moment I'm happy to have the devices working with some empty 500Gb HDD's that I can use when I travel. It would be nice if I could password protect something, so if someone knows a solution for that, I would love to hear it! But for now I can live with the present set-up.