Why is my iCloud storage back up so much larger than my iPad storage size?

I’m trying to back up my iPad but I noticed that my old back up from 5 years ago was over 800gb??? I thought it was a mistake since my iPad device storage can only be 256 gb. So I deleted it and now I’m trying to back it up and it seems to not let me, and the new estimate is still over 800gb. How is that even physically possible if my iPad can only store 256 gb. Is there a solution???

anyone else have this problem?

[Edited by Moderator]