BuddyBoss (BuddyPress / bbPress) moderation filters not doing anything

You’ve got the bp_bypass_if_user_can_moderate arguments wrong. From the documentation you linked to it should be bool $value, int $user_id, string $title, string $content, and as normal for filters you should pass through $value if you’re not going to change it. e.g. here’s a fixed up version of your filter:

add_filter( 'bp_bypass_check_for_moderation',
            'bbp_bypass_if_user_can_moderate', 10, 4 );

function bbp_bypass_if_user_can_moderate( $value, $user_id, $title, $content ) {
    if ( ( !$value ) && ( user_can( $user_id, 'moderate' ) ||
         wc_memberships_is_user_active_member( $user_id, 'premium' ) ) ) {
        return true;
    }

    return $value;
}

I can’t say for sure this will work though.