By default, there is no built-in option to hide the new/activity feed title header on the activity page, and will require custom works. Alternatively, you can use the following CSS code.
Please follow the steps below:
1. Go to BuddyBoss dashboard – Theme Options.
2. Under Custom Codes, enable CSS.
3. Append the following code:
body.directory.activity header.entry-header { display: none; }
4. Save changes.
Here is a side-by-side comparison: