Hi there,
I've tried migrating a portal from Environment A to Environment B a few different ways (XRM Toolbox - 'Portal Records Mover', 'Portal Configuration Deployer' and also Power Platform CLI download/upload following this link: https://learn.microsoft.com/en-us/power-pages/admin/migrate-site-configuration?tabs=CLI#transfer-website-metadata).
Every time I tried migrating, it would overwrite the existing portal in Environment B.
Does anyone have any experience with this?