I've spent an hour now going through every single menu in the entire LibreOffice Writer program, and searching online. There is no way to set it to use page numbers. It lets you select which "style" should be used, and you can manually insert a "page number" into the normal text as a number (which is obviously not what we want), create an empty "footer", but nowhere does it let you set it to use page numbers.
This nonsensical page doesn't explain anything, yet uses many words: https://help.libreoffice.org/6.2/en-US/text/swriter/guide/pagenumbers.html?DbPAR=WRITER
I refuse to believe that "there is no such feature". They must have just managed to hide it extremely well, both in the program and in the manual. Not only is this the most useful and basic feature imaginable for any word processor -- it's one of the easiest ones to implement as well. There is just no way that this isn't in the program. It cannot possibly be that they expect me to manually create a "footer" on every page and manually insert a page number from the menu, or type it in myself.
This is supposed to be a setting that you set for the document. Like a checkbox that you click, called "Use page numbers", and then it will show a "1" in the centre-bottom of the first page, "2" on the next, etc. If this "feature" truly is missing, I'm officially giving up entirely and forever on open source/free software.