Updated 10102022-061841
Hmmm.
If I were in that position - which, if I'm correct, I often am, actually lol - I would probably try to involve Toolbox Pro's folder bookmarks when going for recursion from multiple directories. The crucial difference being - it is capable of recursively listing file references instead of having to actually retrieve the whole folder contents in order to reference it (as Get Contents of Folder does.)
If you really want to choose from all those results within shortcuts, I'd suggest using Choose from List and defaulting to having all of the results selected, maybe?
Hey one thing that has yet evaded my attempts for shortcut actions you may have a solution for. In the files app on iOS one can type Audio.. and the search suggestion of Audio File as a category appears (amongst any other file type as a catalog options given the initial text prompt to start the catagory). This is handy when I want to search all of iCloud for audio files to aggregate every song of mine I store across many different directories in iCloud into a single list of files to browse by date for example. Problem is that iOS does not have the usual action menu UI button to allow for a ‘select’ action to select multiple files with when viewing files from search results (not to my knowledge at least, perhaps you have the solution to this problem too?)
My solution idea was to use a shortcut action to search files using the ‘Audio File’ catagory as the input and have the shortcut action return the files matching the query like it works in the files app as described above so i can generate a single list of filenames from the returned files set to filename property for my reference to use in various automations like generating bandcamp like audio player webpages for new collections of songs or a page with a playlist of every song in icloud)
Any thoughts? I can easily solve this using a-shell and find/grep/sed but would be handy in shortcut form.