flow-talk-page-beta-feature-description is used on the Beta tab on Special:Preferences.
It says :
> Enables a new structured discussion system on your user talk page. Structured Discussions simplifies talk page discussions with clear places to write and reply, and allows conversation-level notifications. This feature is not auto-enabled; users will have to enable it separately.
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>Existing wikitext discussions are moved to an archive. Disabling this feature will move the Structured Discussion board to a subpage and un-archive the previous talkpage. Learn more about activation.
As we work on {{T332022}}, this text should be replaced to invite users to know that the feature will be decommissioned and to invite them to uncheck that Beta feature.
> Allowed you to enable a structured discussion system on your user talk page. Structured Discussions were offered as a test, but they will be soon removed from the wikis. We invite you to consider stopping using this feature.
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>Disabling this feature will move the Structured Discussion board to a subpage and un-archive the previous talkpage. Learn more about deactivation.
Link to deactivation: https://www.mediawiki.org/wiki/Help:Structured_Discussions/Activation#deactivate