Hi,
Your site’s H1 uses GeneratePress’ h1 setting on desktop and Elementor settings on mobile.
Perhaps your H1 in Elementor was specifically set only on mobile and was left by default on Desktop?
Can you confirm this? Let us know what you find.
Btw, when troubleshooting, its ideal to temporarily disable caching plugins so the changes reflects immediately. Also, it is advised to make sure you purge cache every time you make styling changes.
A wise man once said:
"Have you cleared your cache?"