The automatic import to the photos app no longer works. This worked for me...iPad Air3 IOS 17.3.1
Copy the pictures into a folder on the SD card if you are using a PC as the source, a camera will automatically put the pictures into a folder. Plug the SD card and reader into your iPad, open the files app, there should now be a folder called "untitled" or "unnamed". Open this folder, you should now see the folder containing your pictures. Open this, all your pictures will be displayed as thumbnails. Select/select all the ones you want. Hit share at the bottom of the screen, then select save image. This will save the images onto your iPad and make them visible in the photos app.