By default, documents created using HTML are displayed in a single-spaced format. If you want to introduce additional line spacing, ... which introduces a double-spaced paragraph break.

The issue occurs exclusively in Outlook’s HTML mode because of the way the program treats line and paragraph breaks for web-based email clients. SEE: 50 time-saving tips to speed your work in ...

You will find the new option in Docs mobile from the Format button, under the Paragraph tab. Here, you will see the “Add page break before” option alongside a bunch of others.