The iPad still uses the same APFS file system that the Mac does, but files are organized differently.One of the issues with the iPad is the filing system. This may go back to the Newton, which used a "soup" to store files, whatever that meant. On the Mac, files can be in folders within folders. On the iPad (and iPhone) God only knows how the files are stored. I've never managed to download a file on the iPad and get it back, though I suppose that's possible. At least they put the Files app on the iPad so one can get files from Dropbox and iCloud, but if you want to open one of those files on an app, you have to go through all sorts of gymnastics. I don't like Android, but at least it has a much more rational filing system.
On iPad (and on iOS) the files for most apps are siloed to the data folders of those apps. This is a security measure to prevent apps from opening the wrong files. There are ways to share files from from app to another but they are not as easy as just opening a file in more than one app. In general apps are expected to open only their own files.
If you have downloaded files, you should open the Files app on the iPad and look in iCloud\downloads for those file. You can also see other files in the iCloud folders. There is a similar "on iPad" starting point for files that are only on that device.