Although we are working hard to create the best low-code LWC Builder, Avonni Builder has some limitations:
Keep in mind that Avonni Builder helps you build and prototype Lightning Web Components with clicks, not code. You can design and prototype the UI of a Web Component and Avonni Designer is only focusing on the UI part of your Web Component. While you can make it functional and export it to Salesforce, developers will still need to work on the logic part to make your component fully functional. This can't be made only using Avonni Designer.
View all the differences between Avonni Designer and Avonni Builder.