My scroll bar has changed to something called "scroll by page" and I don't know how to set it back to the original behavior.

I'm not sure what you mean... at the bottom I see a box but it doesn't seem to have buttons. The box when I hover shows two arrows or anything seeming to relate to scroll by page. I can't see the little picture on your post Do you have a different "view" setting than "page"?.

What program are you using?

I use WordPerfect, as pertains to this issue. It is easier for me to figure out what is happening when I am writing because you can see the codes and will know what you are doing. I also find Word helpful for some things. I did read something about dealing with this problem in Windows (I have win 11 64 Gb) but I don't have problems with other programs. I think I have the 2020 version.

Thanks.

The point is: your screenshot does not show WP.