The current version of the admin panel can not run on the PHP built-in webserver anymore. Does someone know why?
It never could run with the built-in webserver. There was a note on the learn site that admin, pagination, search and many other plugins would not work with it.
It ‘sorta’ worked but many things were broken. Due to so many issues/questions regarding this we just put an exception in to make you aware that it’s not supported for the admin.