Apple SD card reader no longer functioning ( writing in April 2023)

Having tested both my Lightning and USB-C SD Card readers, I’ve not been able to reproduce your issue. As such, the problem may be with your iPad.

As the problem occurred subsequent to the most recent iPadOS update, it might be reasonable to assume that you have a software issue - that might be resolved with full reset of iPad settings.

Before performing the reset, you would be well advised to ensure that you have a current iCloud or iTunes backup. While no data should be lost, having a current backup is a precautionary measure:

How to back up your iPhone, iPad, and iPod touch - Apple Support

To reset your iPad:

Settings > General > Transfer or Reset iPad > Reset > Reset All Settings

After reseting the iPad, you can again test your SD Card reader.

If the problem hasn’t been resolved, your next step is to perform a full reset of your iPad. This reset will erase all data and settings - after which you can restore your data from your backup. To perform the full reset:

Settings > General > Transfer or Reset iPad > Erase All Content and Settings

This support page outlines restoring your iPad from your backup:

Restore all content to iPad from a backup - Apple Support

Should the problem remain unresolved, a factory restore is recommended. This process will install a fresh copy of iPadOS 16.4.1:

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

After performing the factory restore, you should initially set-up the iPad without restoring from your backup - and test your SD Card reader. This step will test your iPad and SD Card reader in isolation. After performing the test, hopefully demonstrating successful access to the SD Card Reader, you can restore your date and settings from your backup.

Start here:

Connect external storage devices to iPad - Apple Support

Direct import of photos from your camera SD Card to your Photo library is possible - subject to a couple of caveats:

• the SD Card must be correctly formatted as FAT, FAT32 or exFAT (FAT64)
• stored photos are stored within the expected DCIM folder

Import photos using Apple camera adapters - Apple Support

If you are unable to use the direct photo import feature, you can still manually access and copy photos from the SD Card using the iPad’s built-in Files App. To do so, just open the Files App - and in the Sidebar you will see your SD Card in the list of Locations. If necessary, open the sidebar by tapping the sidebar icon at top-left of the Files App Window. Photos can be copied to the iPad Photo Library, or copied to a folder of your choice either on your iPad or elsewhere.