No, in BuddyPress, I can create the notifications, I would just like to offer the user to not receive them if they opt out. Somehow this is difficult, apparently.
Thanks for the reply @shanebp and the idea – but how would I determine whether to show only the filtered IDs or the entire list? I’d still need that info (the GET variable in my approach) to switch between the two bp_ajax_querystrings, wouldn’t I?
In case anyone is interested, this is how I solved it:
Using the first route, I needed to get the $_GET in Javascript and then add it to the bp.nouveau.requestObject when the variable is present. That way the variable is included in the ajax $_POST using the activity-loop template. Then I can simply query for the meta value and only show activities that have the specified value.