I found 2 workarounds; the easier one costs money. (Oops, 3; 2 cost money.)
The paid app Textastic can access hidden files (or at least hidden folders) if you add their parent/ancestor folder as a bookmark.
Textastic has a “Get File” action in Shortcuts that can then access the hidden folder.
I tested by adding my main vault as a bookmark to Textastic and running this shortcut:
Get .obsidian/switcher.json in External FolderVaultName
Get text from File
And it retrieved the contents of the file. So it should be possible to check for the existence of the files you need to know about.
For a free solution, a-Shell Mini has Shortcuts actions can see hidden files. You can bookmark a folder using pickFolder and prove you can see hidden files with ls -a (list files [all, including hidden]). The pickFolder thing might not persist across app restarts so you might need to setup a profile that runs it when a-Shell is launched or something (or not, I’m not sure).
The above-linked thread also mentions that the paid version of Working Copy can see hidden files, and I’ve heard that app has extensive Shortcuts support.
Interesting. I tried a-Shell, but couldn’t get it to work. But I didn’t try very hard.
The problem with all of these, however, is that to require the user to have additional software installed to discover if the user has additional software installed somewhat defeats the purpose. However, it still might be worth a try. Thanks!