How to make Preview default to showing thumbnails for single-page item

I have decided to recode the Automator Quick Action to avoid using the Run Applescript action. What I have written will still pop a dialog stating that Finder wants to control the Preview application. Open the panel below before you click the OK button on that dialog to the Automation section. Then click the OK button and you will see Preview added below System Events.

Note, I already had System Events in here, and you may be prompted with two dialogs when first running this Quick Action: 1) Finder wants to control System Events, and 2) Finder wants to control Preview. Each click of the OK button will add its permission as shown below.

Now, when I select a PDF in Finder and then choose Quick Actions > Use PDF Thumbnails, it works for any selected PDF, just as planned. I changed the name of the Quick Action when I saved it.

This time, I am using Automator's Library > Utilities > Run Shell Script action, and NOT Run AppleScript. Here is what the finished Quick Action looks like:

When you drag the Run Shell Script to the workflow window, and set the shell to /bin/zsh and Pass input: as arguments, you will see new content appear in the window. Select that content and backspace to remove it. Replace that run shell script content with the following code:

: <<"COMMENT"

Select PDF document in Finder and then right-click and choose Quick Actions > Use PDF Thumbnails.
COMMENT

function show_thumbnails () {
	osascript <<-AS
		use scripting additions

		tell application "Preview"
		activate
		open file POSIX file "${1}" as alias

		tell application "System Events"
			tell process "Preview"
				set frontmost to true
				click menu item "Thumbnails" of menu "View" of its menu bar
			end tell
		end tell
		end tell
		return
AS
}


show_thumbnails "${@}"
exit 0

Then save, and name your new Quick Action.

Here is an Automator Quick Action (PDF All Thumbnails) that you right-click on a PDF (any number of pages), and then choose Quick Actions > PDF All Thumbnails from the secondary Finder menu. This will open any selected PDF in the Preview thumbnail view. Tested: macOS 11.6.1.

Steps:

1. Launch /Applications/Automator; New document on Desktop; Quick Action, and click Choose.
2. Drag and drop the Utilities Library > Run AppleScript into the large empty workflow window.
   1. Set Workflow receives current [ PDF files ] in [ Finder ]
   2. Change nothing else in this header area
   3. Select all of the content in the Run AppleScript action and remove it.
   4. Copy/paste the code from below into that Run Applescript window, and then click the hammer icon in the Run AppleScript toolbar.
3. Save: PDF All Thumbnails (the name is your choice but recommend keep it short)
4. Quit Automator

# PDF All Thumbnails.workflow

# Save as Automator Quick Action
# Right-click on PDF file, and from secondary menu, choose Quick Actions > PDF All Thumbnails.

use scripting additions

on run {input, parameters}
	
	tell application "Preview"
		activate
		open file input
		
		tell application "System Events"
			tell process "Preview"
				set frontmost to true
				click menu item "Thumbnails" of menu "View" of its menu bar
			end tell
		end tell
	end tell
    return
end run

I happen to on Monterey 12.0.1 this afternoon and if I open a single-page PDF and choose thumbnails and then quit Preview, all subsequent PDF open with the thumbnail view on, whether multi-page or single-page PDF.

Agreed. There is no user fix for automatic thumbnails on every opened single-page PDF.

I imagine one could write an Automator Quick Action that when you click on a PDF document, it would get the page count, and trigger Preview to enable thumbnails for single-page PDF. I haven't tested this, but seems possible.

On further investigation, one must enable Thumbnails on any PDF, and a subsequently opened single-page PDF will also show a thumbnail. Not having a thumbnail view set on the last PDF viewed, before opening a single-page PDF will suppress the thumbnail view on that PDF.

Did you click the OK button and try running it again?

When prompted below, enter your admin password to gain access to the System Preferences

Otherwise, System Preferences > Security & Privacy panel. Enter your admin password to unlock it, and then select Privacy > Accessibility and add [+] Automator (in your /Applications folder) to Accessibility. Quick the Preferences panel, and try running the script again.