Have you enabled the Click to Play option in the Responsify parameters?

Please see - https://www.joomlacontenteditor.net/support/documentation/plugins/responsify

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The content needs to be processed by the Responsify plugin, which uses the onContentPrepare event. As this is Yootheme content, it is not being processed by the event, so the Full Width Display and Click to Play options are not available.

Is there a Yootheme option to process the content with onContentPrepare?

I can see in my tests that the Yootheme content is being processed by the Responsify plugin via the onContentPrepare event, but for some reason Yootheme is not updating the content it renders with the processed content.

That is why I think there is a setting we are both missing, as I am also seeing the issue on a local test site.

maybe this should be set automatically during installation

Any plugin or extension installed after it would then be the last in the order. Yootheme probably process content using a system plugin, which is different to how it is done in core Joomla, which is why the ordering is important.