Because Extras is built on the Elementor API, it generally has the same requirements as Elementor. So, before anything else, please make sure you abide by these. They are outlined here: https://docs.elementor.com/article/38-requirements.
Elementor requires PHP 7+, but it says it also works with 5.4+. When activating Extras, please make sure you have PHP 7 or greated to avoid getting a white screen.
Because Extras is an Elementor addon, it will not support some older versions of Elementor. However, if you are on an Elementor version that is not compatible with Extras, the plugin deactivates itself when you try to activate it and lets you know what version of Elementor is required.
Some widgets or functionalities that Extras depend on Elementor Pro. If you don’t have Elementor Pro installed and activated, these will not be available but you’ll be able to activate and use Extras without any issues.
Similarly to the above requirements, if Elementor Pro is active, Extras will be compatible with a certain version of Elementor Pro and above. You will get a notification if you are on a non compatible version of Elementor Pro and you should update it to the latest version before activating Extras.