Hi @vorpal,
I hope you are well today and thank you for your question.
Yes you can add more custom social icons by developing CSS code as described in the following reply.
https://colorlibsupport.com/t/social-icon-xing/#post-37560
In the sparkling theme you can use the code shared in the above reply by adding the following CSS code in the Custom CSS option of the latest version of Sparkling theme on the below path.
Admin Area -> Appearance -> Customize -> Sparkling Options -> Other -> Custom CSS
Best Regards,
Movin