Try as I might, the Files app won’t let me add more than 5GB of files even though the Settings app says I have tons of space (this is why I bought a 256GB iPad, after all). I can’t delete anything else because there’s nothing showing up in Files for me to delete and the Settings app doesn’t let me do anything because it tells me I’m swimming in free space. And yes, I’ve gone to “Recently Deleted” in Files to actually remove the things the system hadn’t purged yet.
This specific issue isn’t something I’ve run into myself, but the mysteriously large “other” storage usage problem would frequently plague both my wife and I. Luckily, Apple is a bit more generous with storage capacity than they used to be and that has essentially solved the issue. But iOS and iPadOS clearly aren’t good enough at managing local storage for you and the system should offer some more tools so that we can manage it ourselves.