For any text area set to use the Font Awesome 5 font faces, you can now select one of the Font Awesome 6 font faces for the latest icons. If you check the font-weight menu, you'll see it now has the new Thin style in addition to Solid, Regular, and Light.
Some programs allow you to multi-select text areas to swap them all out between different font faces easily if you want to upgrade a particular file or design to go from Font Awesome 5 to Font Awesome 6.
For Figma, if you select a text item using a Font Awesome 5 font face (Free, Pro, or Brands), you can use the "Select All with the Same Font" action under the Edit menu.
For Sketch, you'll need a plugin like Fontily.
For Illustrator, you can use the "Find Font" action under the Type menu.