Hello AppleLoyalist4,
Let's use the steps below to boot into safe mode to see if that behavior persists from there. Those steps vary depending on the model of your MacBook Pro:
Apple silicon
1. Shut down your Mac.
2. Turn on your Mac and continue to press and hold the power button until you see the startup options window.
3. Select your startup disk, then press and hold the Shift key while clicking “Continue in Safe Mode.”
4. Log in to your Mac. You might be asked to log in again.
Intel processor
1. Turn on or restart your Mac, then immediately press and hold the Shift key as your Mac starts up.
2. Release the key when you see the login window, then log in to your Mac.
3. You might be asked to log in again. On either the first or second login window, you should see ”Safe Boot” in the upper-right corner of the window.
You can also find those steps in this resource: How to use safe mode on your Mac
It can take a few extra minutes to boot into safe mode. Your screen may flash or flicker while in safe mode. Those behaviors are expected. Testing in safe mode runs a check on your disk, removes some cached files, and can help isolate conflicts with startup items. Once you've tested that behavior in safe mode, you can restart to leave safe mode.
Should that still persist, do you experience the same behavior with slideshows that are only videos?
Does this happen with both the Play Slideshow and Create Slideshow options? How about with different themes? Create slideshows in Photos on Mac
Let us know, and we'll keep moving forward from there based on your results.
