Hi Psycho,

You Added the Function, but You Forgot to Call the Function
Add This-

add_action( 'bp_signup_pre_validate', 'buddydev_inject_username_as_fullname' );

Also, I Think The Step 3 Mentioned Here- https://buddydev.com/buddypress-better-registration-part-1-remove-full-name-confirm-password-from-buddypress-registration/ could be Added too.

function buddydev_disable_fullname_required_attributes( $atts, $field_name ) {
 
    global $field;
    $fullname_field_id = 1;
 
    if ( $field && $fullname_field_id !== $field->id ) {
        return $atts;
    }
 
    foreach ( $atts as $key => $value ) {
        if ( 'required' === $value ) {
            unset( $atts[ $key ] );
            break;
        }
    }
    return $atts;
}
 
add_filter( 'bp_get_form_field_attributes', 'buddydev_disable_fullname_required_attributes', 10, 2 );

Hope That Helps..
Cromacio

Hey There,
Just an Update. Try This Too-

body .page-id-01.button.acomment-reply.bp-primary-action.bp-tooltip {
display: none !important;
}

body .page-id-01.acomment-reply.bp-primary-action {
display: none !important;
}

If This too Doesn’t Help You,
Could You Share a Link to the Page where you Use Buddypress Activity Shortcode?
It Will Let me Provide You Better Assistance.

Cheers, Cromacio