I found this answer in an old 2016 post, and I have the same problem.
I encrypted my SD card and when I unencrypted my phone, I didn't realize I needed to unencrypt the SD card first. To be honest, I probably would have forgotten to anyway, I was already so frustrated as I had someone in my phone and this was my latest attempt to get them out.
I was wondering if you needed to use the same phone that you encrypted the card on to do what you are suggesting or can you use a totally different phone.
I have recently given said phone to a friend in another state who had a dinosaur phone. In fact I am trying to get the unlock code for it now.
I appreciate any help as this card contains important data. I realize I should have done backups, but I couldn't at the time.