Hi Kratz,
Thanks for contacting us,
It’s not possible to add icons to the list of icons for the shop and category header page.
The icons are those that are available in the list.
Please provide more detail about which icon do you want to add and the page that you wanna want to have this icon.
Also, please your WordPress login information to me, I will do it for you with a custom of CSS code if possible.
Best Regards.