When you edit a document in Word Online, you may not see any page breaks, at least not clearly. However, if you print or download the document and work with it locally, you'll find that the page breaks are present.

If you are saying that you want to add manual page breaks in the document, you may be able to do that with Find & Replace (not in Word Online, though).

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional