Keep iCloud Drive directory for "offline" use on iPad? I have a directory under the Documents folder (let's call it My Vacation), and iCloud Drive is enabled.

I'm regularly adding files to this directory on my Mac. (PDFs, tickets, etc.)

How can I mark this directory as "available offline" on my iPad, so that I don't have to tap every single file before I leave to make sure they've all been downloaded to the iPad? (I will be without internet nearly all the trip.)

I'd be equally happy keeping all my iCloud Drive contents on my iPad, but there doesn't seem to be a "Keep All Files" vs. "Optimize Storage" option on iOS.
I do not think there is an "Keep Offline" feature on iCloud. I generally hit the download icon next to the files that I would need before I travel. But on iOS13 there is a new pin feature for folders that would keep the folder for offline access.