Cannot enter text in Pages document

You say it is a WP (word-processing) document which does allow direct text input. However, if you chose a Blank Layout template instead of a Blank template, that would explain the inability to enter text. You have a page layout document which is what you get when you select the Blank Layout template.

In a word-processing document, you cannot delete pages from individual thumbnails as you could in a Layout style document. You literally need to select all content on the page to be removed, hit backspace to delete that content, and another backspace to remove the page break. Rinse repeat.

I am a bit puzzled why those three pages in a word-processing document are not allowing you to enter text unless the involved page has a locked shape or text box overlaying the page itself. If that is the case, you would need to select that object and from the Arrange panel, click UnLock. Remove that object, and then perform the first paragraph.