I'll try and help you if I can.
Please can I ask some questions to try and establish a picture of what you have tried to find the folder?
What have you used to try and search for the folder, other than within the Gallery App itself. Have you tried Google Files?
Do you have a cloud backup? Like One Drive, Amazon Photo's or Droo Box thar could have the Photo's saved?
Could the folder have been moved into the Secure Folder at any time? Or even Locked Folder within Google Files?
I'm just trying to get give you some suggestions, if I've helped, great, I'd not, get back, and il keep trying to think where the folder could have gone.
