Small caps formatting is not supported in the static text of a numbered list, as you have noticed. It wouldn't be the same, of course, but using uppercase and a slightly smaller font size may be acceptable.

Using a manual line break in the numbered paragraphs is a perfectly good workaround when you want the heading number and the text on different text lines in the document. Why do you feel it isn't reliable?

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional