app-assets-javascript-calendars.js

const calendar = {
  initialize() {
    const calendars = document.getElementsByClass('fullcalendar');
    Array.from(calendars).forEach(function(cal) {
      const place = cal.dataset.place;
      cal.html(''); // Remove any previous calendar
      cal.fullCalendar({
        eventSources: [{ url: '/events/feed.json?place=' + place }],
        other_options:...
      });
    });
  },
};

document.addEventListener('turbolinks:load', function(cal) {
      calendar.initialize();
});

app-controllers-events_controller.rb

class EventsController
  def feed
    @events = set_events
  end
  
  def index
    @place = params.fetch(:place, nil) 
  end

  def set_events
    if params[:place].present?
      Event.place(params[:place])
    else
      Event.all
    end
  end
end

app-views-events-feed.json.jbuilder

json.events(@events)

app-views-events-index.html.erb

<% form_with(url: events_path) do |form| %>
  <%= form.text_field('place') %>
  <%= form.submit %>
<% end %>

<% if @place.present? %>
  <div class='fullcalendar' data-place="<%= @place %>"></div>
<% end %>

@knzudgt I did not see this reply before.

If you add the feed.json.jbuilder you will not need the index.json.jbuilder.

I think the event_url looks great.