The Salesforce community knows that the LastActivityDate field does not update for all contacts in shared activities. This is a known limitation.
In Salesforce, Shared Activities let you associate multiple contacts with a single task or event. However, only the primary contact, listed in the WhoId field, has their LastActivityDate updated. Secondary contacts don't have their LastActivityDate field updated even though they are associated with the activity and it appears in their activity timeline.
Salesforce's data model handles activity relationships in a specific way, which causes this limitation. The WhoId field links to a single contact or lead. Additional contacts can be associated through the ActivityRelation object. However, the LastActivityDate field does not consider these secondary associations.
There is no out-of-the-box solution for this limitation. However, customers can use these workarounds:
Create a custom field , such as MostRecentActivityDate__c.
Use a Flow, Scheduled Job, or Apex Trigger to:
Read from the ActivityRelation object.
Update that custom field with the latest ActivityDate of related activities, regardless of WhoId.
004637111

We use three kinds of cookies on our websites: required, functional, and advertising. You can choose whether functional and advertising cookies apply. Click on the different cookie categories to find out more about each category and to change the default settings.
Privacy Statement
Required cookies are necessary for basic website functionality. Some examples include: session cookies needed to transmit the website, authentication cookies, and security cookies.
Functional cookies enhance functions, performance, and services on the website. Some examples include: cookies used to analyze site traffic, cookies used for market research, and cookies used to display advertising that is not directed to a particular individual.
Advertising cookies track activity across websites in order to understand a viewer’s interests, and direct them specific marketing. Some examples include: cookies used for remarketing, or interest-based advertising.