The following is a blog entry created by Lisandro in 2017. It shows assorted versions back to version 4. It’s in Portuguese, but you can translate it to English if you want to read it or just look at the pics.
I started using Avast when version 5 was released back in 2010.
https://blog.avast.com/pt-br/mate-a-saudade-das-antigas-versões-da-interface-do-avast