When using the command + n keyboard shortcut (or File > Add New Site), you’re taken to the second step of the site creation process, meaning that you cannot use a blueprint.
Either press the command+n shortcut or go to File > Add New Site. You’re presented with “What’s your site’s name?,” which now seems to be a second step, after you decide to not use a blueprint. “Go Back” takes you to whatever screen you were just on, so there’s now no way to create a site from a blueprint if you enter the dialog using these methods.
If you enter the add new site wizard by clicking the plus icon in the bottom left, you get the choice to ‘Create a new site’ or ‘Create from Blueprint’. The command+n and File > Add New Site methods should land on this page, rather than the second one.
Mac OS X 12.3.1