HI there,
If a new font installation is not showing in the Axure RP font dropdown, what often helps is to try restarting the application; can you test whether restarting or rebooting allows the font to show in the dropdown?
If the font still doesn’t appear after restarting, there could be a problem with the way that the font was installed or activated on your machine. For example, would you happen to be using a font manager on a Windows machine to activate the font? If you’re using a font management tool like that, the best workaround is to manually install the font files directly onto your local computer.
As a caveat, the new Font Awesome 5 icons come in three different font varieties that you’ll want to install directly on your machine. You can see how the icons are broken up into the three categories (Solid, Regular, Brand) here:
https://fontawesome.com/cheatsheet