Unwanted Blurred image surrounds some slides in photos app slideshow

Hi,
I’m putting together a folder of family history photos and want to use Windows 11 Photo App’s slideshow to display them. I have 2 questions.
1) I have scanned them and sometimes cropped / added a text box which is good, but I prefer if the areas beside narrow images were black or something else instead of a blurred image of the photo. They distract and take away the focus of the viewer.” Is there a way to turn off the blurred space fillers in slides where this happens?
2) Also, how can I make the time between slides a bit longer than the pre-set interval?

To clarify - I have an album of pictures and go in, click on the picture and execute the slideshow function to play on screen or when connected to a TV. I am not talking about a slideshow that plays as my desktop background (which seems to be all I can find help on), but a slideshow I want to run as I explained above that is independent of my desktop background.

I would very much appreciate some help on this.

Steve.