Ok so my further testing the error message you were getting when you tried to add new page is still happening with all plugin disabled
Also, I have tested with all plugins disabled it works, pro works with warzone the plugin that keeps making it jump back to > "Howdy! What would you like to launch?" is WooCommerce it the only plugin I am not able to use the builder in.
Is WooCommerce not supported by pro? or the builder?
I Have left everything as it for your further testing
Login in details are the same as above I've not removed login for your testing same for FTP as well