Create Slideshow with Photos in Random Order.

Photos does not yet have a tool to do this.

When I need a random slideshow, I add the photos to a top level album, then shuffle the photos in the album using an Apple Script, then use this shuffled album as a source for the slideshow. For an example script, see: Script: Shuffle Photos for an Instant Slideshow 2018

Usually, I also want to see the titles, dates, and locations for the slideshow - then I am using this script: Script: A Slideshow With Titles and Locations And Dates in Photos

And for the shuffled version: Script: A Randomly Shuffled Slideshow in Photos with Titles as Notifications

A quick and dirty solution would be to set your album as the source for the screensaver in the System Preferences > Desktop & Screensaver. Then make the screensaver shuffle the pictures randomly in the Options and let the Screensaver present your slideshow. The slideshow screensaver is a bit buggy on the current system version, but it should work well in macOS 10.15 Catalina.

Workaround: Most Photos slideshow "styles" or "themes" exist as Screensavers, too. Find the style you want in System Preferences -> Desktop & Screensaver -> Screensaver, choose the Photos album you want, then check "Shuffle slide order."

Only downside is you must keep the screensaver active as long as you want to present your slideshow!

I just went through a rabbit hole trying to figure something out for this exact issue. I just had a light bulb moment realizing I had a free tool all along and had to share. You can use VLC player.

You just need to make sure to first go to the settings in VLC and hit the show all button to pull up more detailed preferences. Once the menu is expanded go to playlist and turn on the play files randomly forever option.

Then in the playlist where all the files are loaded right click and select shuffle playlist. You can shuffle it as many times as you want. Then hit play.

Sadly, you used to be able to randomize with iPhoto. It's only since Photos that the randomization has become an issue. I have over 11K photos in my collection and while I am able to randomize to a degree, it seems that the same number of photos are used every time, possibly in the same order as well, although I haven't tried to verify that. I see pictures from roughly the same timeline played over and over so matter when I view the slide show.

1. Laptop: Grab an external USB mouse, and set the trackpad to disable when external mouse is present. Desktop: disconnect the mouse.
2. Set your screen and machine to NEVER sleep or turn off display.
3. Set your timeout for screensaver to 1 minute (or sooner if possible).
4. Set your system to lock immediately after screensaver starets and require a password to re-enter (good for kiosk/unattended setup).
5. Make sure the laptop is powered/plugged into the wall during the presentation.
6. Close all unnecessary programs while presenting, enter Do Not Disturb mode and disable notifications on the lock screen/screensaver.

You mean this one?

https://www.videolan.org/vlc/

Clicking on the download button will give you the version for your OS.

You're welcome 😊

Hints on keeping screensaver active?

VLC won't have any of the effects I believe OG poster was hoping to use, via "Photos" app.