Name and Related To fields missing in Task Feed Tracking field options
|Knowledge Article Number||000220096|
Check if " Allow Users to Relate Multiple Contacts to Tasks and Events" feature is enabled.
1. Go to Setup.
2. Under "Build", click Customize | click Activities | then click Activity Settings.
If "Allow Users to Relate Multiple Contacts to Tasks and Events" (Shared Activities feature) is checked, Name and Related To fields won't be available in the Task Feed Tracking field option.
To disable Shared Activities, you'll need to submit a ticket to Salesforce Support.
Heads up - Reverting shared activities can cause data loss specifically for existing tasks and events that are associated to more than one Contact or Lead. The contact/lead relationship to the task or event will be gone but the Contact or Lead will not be deleted.