Help SD Card Encryption Broke Photos

When you encrypt any kind of storage media it's not a simplistic process like renaming a folder, it's a change to the file system itself that involves formatting the base file structure. Whatever data that was on your microSD card previously has been deleted and in a permanent way -- now that the card is encrypted, old files that were stored on it are no longer accessible even with the magic file recovery utilities that claim to restore anything. And new files you save to the card will reside on the now encrypted media, so even if you pull the card out and mount it on a computer, any data on the card will appear to be scrambled gibberish when accessed. Regarding trying to decrypt the card, the data was wiped during the encryption process, there are no files that can just reappear. Encryption >< decryption isn't just a matter of switching between one state or another, it's a fundamental change to the storage media a low level.
But getting back to those lost photos, if you had set up something like the Google Photos app to automatically backup and sync your photo library into your online Google account, your photos should still be accessible. (The Gallery app does not include that function). Or if you had previously set up some kind of automatic backup solution into other online storage services like Dropbox, OneDrive, etc. than check those. But recovering files off that now encrypted microSD card isn't an option.
This comes off as preachy and dismissive but from this point on be sure you have set up a good backup solution for anything you want saved on your phone. Smartphones are not reliable as long-term storage.
Another option is to set up Samsung's Smart Switch utility, which includes functionality to do full back ups. If you lose your phone or need to do something drastic like a Factory Reset it also makes doing a restore less of a hassle.

no need to back things up daily. google photos automatically does it for you. i never have to back my photos up to my pc.