I did an experiment. I Tried to put page numbers in the footer in a blank document without any formatting, text, typing, etc… exactly as it shows here: Inserting Page Numbers in Footers
but it did the exact same thing. The same problem I originally had.
So obviously your program is broken and its not me doing something wrong or not knowing how to use it.
Perhaps you could show the sample document so someone can try and see what has happened.
I could find no page number in the footer or elsewhere in that document. I’ve added page numbering using Insert - Field - Page Number and added the word Page before it. The numbering increments with each page.
Untitled 2_pageno.odt (45.3 KB)
I gave you what you asked for.
Thank you. I’m done here.
Have a nice day. 
Please upload a sample file with YOUR inserted page numbers inside.
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Didn’t work. Only one page number showed up and on one page and its in the corner at the top not the footer.
Untitled 1.odt (9.0 KB)
That is because the page number is on the page body, not in the header.
Quoting from the help page you linked above:
To Insert a Page Number
Choose Insert - Header and Footer - Footer and select the page style that you want to add the footer to.
Choose Insert - Field - Page Number.
I’ve followed those steps in your supplied sample document; the result is attached. The numbering continues on page 2.
Untitled 1a.odt (9.5 KB)
I don’t think I can explain it more simply than that.
there are discussion about providing videos : https://community.documentfoundation.org/t/documentation-team-meeting-minutes-friday-october-3rd-2025-15-00-utc/13280#videos-15
maybe @Hrbrgr can expand a bit where this was apparently left years ago : Video how-to guide - The Document Foundation Wiki
