Password-protected folder DISAPPEARED

Hi everyone. About a year and a half/two years ago, I created a password-protected folder in Disk Utility (.dmg) to store some files. It worked perfectly this whole time; I would search for it in Finder, select it, enter the password, and access it. All that until today.

For some reason, when I tried accessing it today, it does not even show. Out of nowhere. I search for it in Finder and it is as it had never existed.

I had very important info in this folder and I am desperate to recover it. Do they maybe expire if not open after a while? Besides that, the only correlation I can think of is updating my Mac, but I have done so before and this did not happen.

Does anyone know how to help?