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Or do I need both installed. Thank you!
Important: Do not activate until you have nulled the plugins.
You need both installed. First, install its free version. Check my post about how to null Elementor. Make the necessary modifications to the free version 3.0.11 (free version) and activate.
Then, you can install Elementor Pro 3.0.5, make the necessary modifications (there are three files that you have to touch) and then activate.
Voilà! It works!