The concepts of how to do this have not changed since Word 5.0 on the Mac (1992).
Location of some controls have changed. So, the tutorials you have found should be instructive and if read should show you the answer. Here is the one I go to: How to put a portrait page number on a landscape page by MVPs Bill Coan, Suzanne Barnhill, and Dave Rado. That page is for the Windows versions, but again, the concepts are the same.
I assume that you have already created the landscape section and have disabled different first page and link to previous in the header and footer for that section. I assume that you already have the portrait section to follow and likewise disabled the link to previous and different first page settings in that section.
- Return to the landscape section.
- Go into the header or footer for editing.
- Create a Table, Text Box or Frame where you want your page number
(without any borders).
- Double-click in that and insert a PAGE field. You can do this by
typing the word "Page", selecting it, and pressing Cmd+F9. (On some
models you will need Fn+Cmd+F9.) Then F9 or Fn+F9. (The keyboard shortcuts for this are different on the Mac than in the Windows version, although related. Here is a link to my table of shortcuts dealing with fields in both the Windows and Mac operating systems.
- If using a table, rotate the text inside the table. If using a
TextBox or Frame, rotate it with the text.
Here is a link to a demonstration document I prepared a couple of years ago. Demonstration of Portrait Headers and Footers in Landscape Sections. I updated it today for you. It contains one landscape section with portrait-oriented headers and footers using Textboxes and another using Frames. I do not know if the Mac version has rotating shapes with text (the Textboxes) but I am confident that you can use Frames. It has settings for different even and odd headers and footers. Here is my Recap of Header and Footer Settings in Word.
This is not simple or easy, but it can be done!
See also my longer answer in this question.