Adding pages to a design is only available for Lightning Application, Lightning Flow, Communities, Dashboard and Standalone App design types.
IMPORTANT: if you're not seeing the + New page button, please create another design by choosing one of the design types that support this feature.
Check this article to copy content from one design to another one.
NOTE: Design types that support the +New Page button.
You have choice to create different types of pages:
Starting with a blank design can be daunting. Luckily we have created several page templates to help get you started.
For example, if you want to create a record page for an account, you can choose the Account template and Avonni Creator will create the default Salesforce Account page as a prototype with all default fields.
Select the layout you want for your page. You can choose from up to 4 different layouts:
Lastly, give a name to your page. Optionally, you can create the associated tab for your new page.
View all the differences between Avonni Designer and Avonni Builder.