Winter '19 introduced the Case Feed Everywhere feature in Lightning Experience.
This change allowed the standard Lightning Chatter Component to leverage compact feeds for the Case and Social Post objects in Lightning Experience applications.
The Winter '20 enhancement, Respond to Customers Faster with Social Quick Action for Leads made the compact feed for feed-based layouts in Lightning available for the Lead object as well.
This article explains how to change Case Chatter behavior in Salesforce Lightning Experience for Console or Non-Console-based apps. Administrators can request Support to enable or disable compact feed for feed-based layouts on Lead, Case, and Social Post objects
Please ask Support to reference the internal information section of this Knowledge Article # 000352121 and carefully review, acknowledge, and provide the following details to help expedite your case request:
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