When using the See only free/busy (hide details) sharing option in Google Calendar, only events marked as Busy will appear to anyone viewing the public link, including our widget. Events marked as Free will not show up at all.
You can confirm this by opening your shared calendar link in an incognito/private window.
To check this on your side:
Open one of your events in Google Calendar.
Click Edit.
Under the Event details > visibility and availability settings, make sure the event is set to Busy (not Free).
You can also set the event as Busy when creating the event.
If the event is set to Free, it won’t display as Busy when using the See only free/busy sharing option.
The app can only display what Google makes available through the public link.