If you have downloaded a zip file/folder and don't get the option to unzip it on iPad
Then just tap and hold the zip file or a folder
And then drag the zip file into "On my iPad" folder
Again, in "On my iPad" folder tap and hold the moved zip file
Now you will get the option to Uncompress the zip file at the bottom
So, the trick is to move the zip file to "on my iPad" to unzip it
To compress the unzip file again just tap & hold the uncompressed folder
And, tap on "compress" to zip it again