How do I restore disappeared files on my iPad?

I use the files app on my ipad to annotate pdfs all the time and have been doing so for a very long time, but today when I opened the files app I noticed that all the files that I have downloaded in the past 2 months disappeared.

These files contained all my notes and study materials and I really need them.

I don’t have iCloud sync on. And I know these files were there on my Ipad yesterday.

I also say someone here suggesting to update the ipad but i did and that didn’t bring back my files.

[Re-Titled by Moderator]