By default, we do not have this option. You can use the following function and CSS code below. 

Please see the steps below:

Note: Make sure to have a complete site backup before proceeding

    1. Go to Appearance - Theme Editor.

    2. Under Select theme to edit, choose (BuddyBoss Child/whatever theme is active), then click Select.

    3. Below Theme Files, select Theme Functions (functions.php).

    4. Append the code just before the closing PHP tag “?>”:

add_filter( 'bp_activity_do_mentions', '__return_false' );

    5. Click Update File to save the changes.

After that, please follow also the steps below:

    1. Go to BuddyBoss - Theme Options

    2. Under Custom Codes, enable CSS

    3. Append the following:

.atwho-container {
    display: none;
}

Note: Any modifications are considered as custom work already. Know more about our Support policy here: https://www.buddyboss.com/support-policy/