Hello, glad to help you fix this problem.
It's a pity that iPadOS/iOS is unable to directly access encrypted storage devices. Because some proprietary devices that use an installable companion App on the iPad might be able to access passwords.
If you need to share the device between your iPad and PC/Mac, the storage device must be formatted appropriately. Supported devices for iPad have only a single data partition, and it must be formatted as APFS, APFS (encrypted), macOS Extended (HFS+), exFAT (FAT64), FAT32, or FAT.
Maybe it is in other formats. You are suggested to use some professional tool to recover and backup the drive on your Mac like iBoysoft Data Recover for Mac, then format your drive to supported formats and use it on your iPad again.
Also read: How to Format a USB Drive on Mac to the Best Format.
