This site configuration is outdated and needs to be upgraded:
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You can add another Plone site to the server.
Starting with Plone 6, 'Create a new Plone site' applies a profile and creates default content for the new React based default frontend Volto. You are however required to set up and run an additional frontend service to use this setup.
The 'Create Classic Plone site' button creates a Plone site configured for HTML based output, as was already supported by previous Plone versions. Please consult our developer documentation overview for more information about differences and requirements for these frontends and possible upgrade paths from older Plone versions to Plone 6.