BuddyPress.org

To be honest just put in the theme files probably is the lightest / speediest solution. Google lets you know where in the code to place things – put that in the footer.php before the closing tags it says.

But, if you are using the default theme for BuddyPress you probably either want to do a child or you want to use a plugin.

I’ve not tried it but perhaps: https://wordpress.org/extend/plugins/google-analytics-for-wordpress/ works – after all if it’s just inserting into the theme files….