Hey @chasteyn,
Thank you for your feedback.
We have not moved any functionality that was previously free behind a paywall. Keyphrases are part of our new TruSEO content analysis feature. You might be confusing keyphrases, which are only used for the content analysis and are not output in the source code, with meta keywords. You can still add meta keywords in our metabox under the Advanced tab. If you don’t see a setting for meta keywords there, you might need to enable support for them first under General Settings > Advanced.
Here are two of our documentation pages that explain the difference between keyphrases and meta keywords in detail –
https://aioseo.com/docs/using-the-focus-keyphrase-to-analyze-your-content/
https://aioseo.com/docs/keyword-settings/
Let me know if you have any questions!