Today's update broke the UI...

This morning Avast Premium needed to restart my desktop. Once done, the UI will not load anymore! Can someone tell me how to fix this? Thanks.

Have you done at least one Restart (not shutdown/startup cycle) since for good measure.
Also see this:
https://support.avast.com/article/Troubleshoot-Embarrassing-UI-Failed-load

Perfect - You’re a rockstar in my book Rocksteady! Thanks! 8)

Glad to help. Thanks for feedback.