Unable to set numbering to paragraph style in LibreOffice Writer

I am editing Heading 1 style wishing to set numbering, but can't due to the strange message

This option is disabled when chapter numbering is assigned to a paragraph styling.

How to enable?

Go to Tools > Chapter Numbering. By default, Heading 1 is set to use the chapter numbering options described there.

To get headings that look like "1.2.1 The Next Section" you can select 1 - 10 and set Number to "1, 2, 3, …"

If you do not want to use chapter numbering in this way (although I'm not sure what the use case would be for that), then set Paragraph style to None for Level 1. Then the Numbering style for style properties can be modified.