feed.html

<form action="{% url 'mark_as_read' %}" method="post">
    {{ mark_all_as_read_form }}
    <button>Mark all as read</button>
</form>

{% for user_item, mark_as_read_form in user_items_forms %}
    {% include "item.html" with item=user_item.item %}
    <form action="{% url 'mark_as_read' %}" method="post">
        {{ mark_as_read_form }}
        <button>Mark as read</button>
    </form>
{% endfor %}

views.py

def feed(request):
    user = request.user
    user_items = UserItem.objects.filter(user=request.user)
    
    mark_all_as_read_form = MarkAsReadFormset(user=user, queryset=user_items)
    
    user_items_forms = [(ui, MarkAsReadFormset(user=user, queryset=[ui])
                        for ui in user_items]
                        
    return render(request, 'feed.html', {
        'mark_all_as_read_form': mark_all_as_read_form,
        'user_items_forms': user_items_forms})
        
        
def mark_as_read(request):
    user = request.user
    # TODO validate that the UserItems are owned by the user!
    mark_all_as_read_formset = MarkAllAsReadForm(user=user, data=request.POST)
    if mark_all_as_read_formset.is_valid():
        mark_all_as_read_formset.save()
        return ...
    else:
        barf