You need to download and install JCE Pro - https://www.joomlacontenteditor.net/downloads/editor/pro/latest
The Subscription / Download Key enables future updates of JCE Pro, it does not "activate" JCE Pro.
To set the Subscription Key in Joomla 5.2, please see - https://www.joomlacontenteditor.net/support/faq/subscription/using-the-subscription-key#joomla4
Ryan Demmer
Lead Developer / CEO / CTO
Just because you're not paranoid doesn't mean everybody isn't out to get you.