Yea, there’s an issue with that plugin and the new dropdown arrows – I have to find a workaround.
Luckily, the plugin isn’t really necessary. You can add the icons directly into your menu items like this: https://generatepress.com/forums/topic/problem-after-update-where-to-get-old-version/#post-169352
Then you can deactivate the plugin and your menu will be back to normal.
Sorry for the inconvenience – I didn’t even know that plugin existed before today.
Let me know if you need more info 🙂