page attribute – not all parent/categories showing

Hello, I have added a series of new categories and have created new pages and posts. I am having no problem assigning a parent category to posts, but I am having trouble assigning a parent to pages … namely, the list of parents is limited.

I saw that others had this issue and that some were able to scroll down this list or reduce the size of the window to make the scroll bar appear. Neither of these solutions are working for me.

Firstly, it is my assumption that all categories created are considered possible parents. Is this assumption correct?

Secondly, it was suggested to deactivate all the plugins to see if there is a conflict. If I deactivate a plugin, and later reactivate it, is there a risk of losing any settings that have been configured for that plugin? This is a team project and I did not configure the plugins on this site, and don’t want to undo any work done on plugins by other team members.