Leon9x yes, you can add the modifier with a space after the icon name.
For example fas fa-spinner fa-pulse
Make sure to use the documentation for FontAwesome v5 though, only those animations will be available https://fontawesome.com/v5/docs/web/style/animate
I see there are some new animations in v6 but Flarum is not using v6 yet.
You need to switch the documentation to v5 to see the correct 3-letter style prefixes. When viewing v6 documentation it shows the new prefixes which aren't supported in Flarum yet.