How to Shuffle photos in Apple Photos app slideshow?

I'm going to reply to myself here because I found a solution by putting a couple things together. Essentially, out can sort an album by date either-direction, which doesn't help at all, or by Title. So, what if we gave the photos in our album random titles and then have the album "Keep Sorted by Title" and then create a slideshow from that? Well, that works, at the expense of having random titles generated.

There are various ways to deal with the random titles. If you don't use titles, you can select and blow them all away after you're done with this process. Or you could create a temporary Photos library containing copies of the photos you want in your slideshow album just for the purpose of slideshow creation -- I did this using PowerPhotos (from Fat Cat Software).

So, how to get random titles?

Most of the information I needed was here: https://discussions.apple.com/docs/DOC-250000346

I followed those directions to create a script with Automator that was a Service (it's now a "Quick Action" type when creating a new Automator document). I named mine "Random Title Image Selection" when I saved it in Automator. Then I was able to start Photos, select the photos in my album that I wanted to shuffle and choose menu item "Photos" -> "Services" -> "Random Title Image Selection" and random titles were added to my photos. I sorted by Title and then created my slideshow project which used that order. Success!

Here is the AppleScript that I used in Automator:

on run {input, parameters}
	
	tell application "Photos"
		activate
		set imageSel to (get selection)
		if imageSel is {} then
			error "Please select an image."
		else
			repeat with im in imageSel
		        set ranname to random number from 1000 to 9999
				set the name of im to ranname				
			end repeat
		end if
	end tell
	return input
end run

Yes, there could be duplicates, but that doesn't really matter to me and my couple-hundred slide presentation. Using a higher-range like 10000 to 99999 would make that less likely if I wanted. Note: after you run this, if you want to pick the placement of specific images, then just change their title so they end up where you want in the sort. For example, I had a particular image I wanted first, so I just re-named the title 100.

Apple should certainly make this easy, but I hope this answer helps someone else who has the same issue today.