The option to create Power Apps Portals through the New app button in the Power Apps Maker portal has been removed. Instead, there is now a dedicated Power Pages maker portal for Power Pages development. However, if you want to create a site using an existing website record, there is no option to do this when you provision a new site using the Power Pages maker portal. The workaround is to go to the Power Platform Admin Center, select Resources->Power Pages Sites and click into the site you want to point to the website record. Click Edit, select the website record you would like, and click Save.
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