What you experience is a consequence of your misuse of styles (according to the video).
First of all, paragraph style Heading is not a heading style, despite its name. It is a “dummy” style intended to define default appearance of all “operational” heading styles like Heading n but also Contents Heading or Title. Usually, one need only define the heading font, which can be done either in Heading (per document definition) or in
Basic Fonts (Western) (definition valid for all documents of a user unless overridden in Heading, because this setting in stored in user profile).
When you modified your Heading style, you should have noticed its level is
Text body, meaning it does not participate in TOC (and therefore is not “technically” a heading). Assigning a numbering style turned it into a paragraph style suited for numbered list.
Enabling heading numbering is done with
Chapter Numbering. This dialog allows you, from a single location, to customise and tune your numbering hierarchy and formatting.
Note that assigning a numbering to a level does not presume that other levels will have the same numbering or even be numbered. For instance, the first level may be numeric, the second alphabetic, the third bulleted, ad libitum. You can repeat the previous level number or not (I advice you to be consistent: if you repeat the previous numbers, do that on every level otherwise readers will get confused).
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