Running shell scripts in Shortcuts app - can't select "Shortcut input" option

I'm using the MacOS Shortcuts app to create a Finder Quick Action that runs a shell script to run ExifTool. But I can't select the input to my shell script using the Input dropdown. Every time I choose the "Shortcut input" option from the dropdown, it disappears (i.e. doesn't stay selected but resets to blank).

1. ExifTool is installed and working on my system (via Brew).
2. Action is set to receive media files Input (Images, media files, PDF) from Quick Actions
3. The Privacy tab options are set to "allow this shortcut to access Shell", and "Allow Run Shell Script to access Finder"
4. Next in sequence is the Run Shell Script action. Shell is set to "zsh", Pass Input is set to "as arguments".
5. The shell script is as follows (calls exiftool on selected files to remove EXIF metadata):

for f in "$@"
     do
         exiftool -all= -overwrite_original "$f"
     done

When I attempt to run the shortcut, I get an error. "command not found: exiftool"

Running "exiftool -all= somefilename.jpg in Terminal works just fine.

un/checking Run as Administrator makes no difference.

See attached image for shortcut setup: