@ridle Thanks for the report.
That particular problem appears to be caused by some unexpected options data for the plugin in your WordPress database. While the error is thrown by some of the new code for the block editor support, it would be caused when the plugin can’t figure out what version of Font Awesome you’ve configured to use.
That’s a more fundamental problem that would impact other features of the plugin as well. It might occur when the state of the plugin’s options in the database gets corrupted somehow, maybe doing some kind of database migration or backup/restore that went awry.
It may resolve the problem to simply re-save the plugin’s options. If you’re in “Use CDN” mode, you could select a different version, save, and then re-select whatever version you had before, and save again. Of if you’re in “Use Kit” mode, you could “refresh kits”, pick a different kit, save, then go back and pick your original kit and re-save.
If that doesn’t work, then it may be necessary to do a deeper clean of the plugin’s state in your WordPress database. The easiest way to do that is to deactivate and uninstall the plugin (using the controls in the plugins dashboard, so the plugin’s cleanup code runs). Then re-install and re-activate.
Try one of those and let me know?