Capitalizing not displaying well at mobiles

This isn’t a Gutenberg problem, this is a theme issue. You are using Storefront parent theme, and then a customised child theme of Storefront.

Storefront and/or your child theme does not provide a styling for drop cap to match your theme styling settings.

You should either speak to your child theme creator, or feed this back to the Storefront theme development team. Or you can try to fix it yourself, using custom CSS. You should be able to add custom CSS under the Customiser.

If you add the following custom CSS it will change the size of the drop cap first letter on screens small than 1000px wide:

@media (max-width: 999px) {
 .has-drop-cap:not(:focus):first-letter {
 font-size: 3.4em;
 }
}

I see! Thank you very much for the information and the code. It worked perfectly, but I also learnt a little bit more.
??