render_content hookspec is not applied if calling the page.content directly outside of site.render or site.render_collection

[kjaymiller]

As of v 2023.6.1 - The render_content hookspec is now called on parsed content. This means that you are modifying the rendered html and not the pre-existing content. This ensures that plugin developers don't need to think about the content's base type and instead can focus on the ensured HTML-formatted string.

That also means that if you are calling the content elsewhere then you are not getting the plugin's changes but the base-rendered content.