Hi Alexander,
Thank you for writing in and sorry that the icons are now look bolder.
To clarify, this is not an issue with the theme. As you can see here, the latest FontAwesome 5 only provides the Solid (thickest) icon version as Free, the Regular and Light version are part of the FontAwesome 5 PRO, which requires a license from FontAwesome to used.
Don’t buy a FontAwesome 5 PRO license yet, we don’t have an option to integrate that easily
If you really still want to load the FontAwesome 4.7 (light icons) to all your pages. You can use the CSS link provided by BootstrapCDN here.
Then import that to your child theme’s style.css file using the CSS @import Rule. (Just be mindful that you have this on your child theme, as this might create a conflict in the future.)
Hope this shed some lights,
Cheers!