I'm using Collector for ArcGIS 20.2.1 on iOS 13.4.1.
I am trying to follow the directions to sideload via OneDrive and the Files app instead of using iTunes on a laptop that is connected to the iPad.
I got the vtpk onto my iPad via OneDrive and was able to copy it and paste it into the Basemap folder of Collector. It did not show up in my offline basemaps.
I then did the same vtpk via iTunes and noticed that it creates a folder with a guid name and puts the vtpk inside there, and that in iTunes you drop the file at the Collector level rather than in the Basemap folder. It showed correctly in my offline basemaps in Collector
So in Files on the iPad I copied the vtpk to the Collector folder. When I re-browsed to the Collector folder in Files, it had moved into the Basemaps folder inside a new folder that was auto-named.
However I still can't see the basemap in Collector, even though, to the eye, the result in the file structure looks like what happens from iTunes.
Not sure what to try next.