Shortcuts: “Get contents of folder” action does not work with cloud drives

I want a shortcut that lets me choose something from a list of sub-folders within a folder I specify.

This works if the target folder is on my iPhone.

When it’s on my iCloud Drive, it just hangs on the first step.

When it’s on a third-party cloud drive such as Dropbox or Microsoft OneDrive, I can’t even select the folder (the “Open” option is greyed out).

Why is something so seemingly simple so difficult to accomplish when it’s a cloud drive?