You are getting this error message because you are trying to install Elementor as a theme while it is a plugin.
You must install it through "plugins" and not through "Appearance> theme" in your WordPress Dashboard:
https://docs.elementor.com/article/14-installation
https://docs.elementor.com/article/102-installing-elementor-pro
Also note that you also need to install Elementor for free for Elementor Pro to work since the latter is an extension of the former.
