Hi Mike,

Let me explain something:

1. SP Page Builder uses Font Awesome Free 5.15.1 - until webmaster would not disable loading FA in SPPB options.
2. Your template Newsberg loads Font Awesome Free 5.15.2
3. Icons in MegaMenu are from Template, not SPPB.
4. Icons in Menu should be choosed from the list, not added manually. Then CSS is not needed.

As you see both products load new FA 5. But indeed, the only missing part was the code that Ariba gave you already. But to improve icon appearance I suggest small correction:

.fa-broadcast-tower::before {
    font-family: "Font Awesome 5 Free";
    font-size: 20px;
    padding-right: 5px;
}

after