I had to send my Galaxy S20+ for repairs and had to back everything up and factory reset beforehand. I inserted an SD card and backed up to that (using the Samsung backup feature). Now when I try and restore the data, the phone recognises the SD card and I can see the encrypted backed-up files in the file browser, but Samsung & restore says "no backup data". How can I fix this?
When you backed up you should have decrypted the card as the decryption key, which is in the phone gets wiped. So, you now have a phone which has the wrong key for the card.
However, do the following
Copy your SD card to your PC Format your SD card in the phone Encrypt SD card Connect card to PC and copy the data you backed up previously to it. This may take some time. When complete you have a backup your phone can read.