The age of an external hard drive is typically not the reason why it is read-only on an iPad Pro. There are 2 main reasons why your external hard drive shows read-only and doesn't let you add new files to it.
Your external hard drive uses the Microsoft NTFS file system. Apple has introduced NTFS support in iPadOS 15, but it only allows for reading, not writing. Connect your external hard drive to your PC or Mac and verify its file system.
Verify the device's file system on Windows:
- Connect the external hard drive to a PC and open File Explorer.
- Right-click on the disk and select Properties.
- Click the General tab and you will see the file system type of the external hard drive.
Verify the device's file system on Mac:
- Connect the external hard drive to a PC and open the Disk Utility.
- Locate the external hard drive and select it.
- The file system format will show up in the right pane under the name of the device.
How to fix:
To be fully compatible with iPadOS, the attached external storage device must be formatted to FAT, FAT32, exFAT, APFS, or HFS+ with a single partition. You can format an external hard drive on Windows or format an external hard drive on Mac with an appropriate file system. Once this is done, your new iPad Pro, including the latest M2 model, will have both read and write access to the external hard drive.
If your external hard drive is a traditional Hard Disk Drive (HDD) with spinning platters and relies on power from the USB connection, it's probable that the iPad may not be able to supply enough power to operate the HDD. HDDs typically have high power requirements that could exceed the capabilities of the iPad's USB-C port.
How to fix:
If your mechanical hard drive includes its own power adapter for self-powering, you should connect your external hard drive to a power source using that adapter. Alternatively, you can utilize a powered USB hub to connect the HDD to your iPad Pro. In this setup, you'd connect the HDD to one of the hub's data transfer ports and attach a power source to a separate port to provide the necessary power supply.