Unable to select Change Picture every 30 seconds

When I go to system preferences > desktop pictures, and select one, the option to change picture every 30 seconds is greyed out, making unable to be selected.

I did some investigating and this is what I found.

1. On the left side, there are a list of options:

a. a folder of desktop pictures

b. an icon titled colors

c. then the options to select pictures and folders.

2. When I select the desktop pictures folder, the change picture every 30 seconds option is greyed out

3. When I select the colors, pictures, or folders options, I can select to change the picture every 30 seconds.

4. If I double click on the desktop pictures folder, all the images are formatted as either .madesktop or .heic

5. Within this folder is the colors folder. Inside there, the color files are all .png files.

My conclusion is that only .png and probable .jpg / .jpeg files enable the change picture every 30 seconds option, but I was unable to change the format.

So my question is how can this be fixed?