So the Nouveau Site uses Elementor for the Page Headers, and the H1’s Typography has been set directly within the elementor editor. Hence the reason the Customizer does not override them.
You need to edit the pages directly in Elementor and change the H1 settings.
If you want to control them from the Customiser then in Elementor Settings you can Disable Default Fonts. And then edit the pages and replace the current Heading elements with new ones. They will then use the Customizer settings aside from the Line-height which Elementor over rides.