Hi @ClarenceK! Yes, this is part of the (hotly debated) updated interface designer experience. To edit interfaces, navigate to the "Interfaces" tab (as you just did), then click on the name of your base in the top-left corner of the page (the name will have a little down arrow next to it). The first option will be "Edit" with a cogwheel next to it. Click that option to enter the interface editor, and you should be able to add/edit interface pages in the panel that opens on the right-hand side of the page.
If you don't have the "Edit" option, there's a chance your permissions changed, in which case you should reach out to your workspace admin. Linking the interface designer support article for further reading. Let me know if that works!