Hi silverfox93,
You actually don’t want to set font-display to ‘swap’ for an icon set. That’s just for text where you can fall back to a system font. Setting it to ‘swap’ would actually break things.
The proper value would be ‘block’, which is what the default value, ‘auto’, uses.
So there isn’t actually any negative impact on the user from not having that declaration.
If you wanted, you could overwrite your font awesome font face declaration and set that font-display:block explicitly, but the only purpose would be to make Page Speed Insights happy, it doesn’t actually make any real-world difference ??