Search your FULL Google Calendar online.
On your phone, you have normally only a certain time frame of Calendar events available for search by the standard Calendar App.
On the other hand, if you use the Google Calendar Web App, you can search everything, but not very comfortable.
With this App, you can search everything, because it searches online, instead of on your phone. Also, you can search for part words, if necessary.
Tap on a found event, to open that day in the Calendar App.
You can also configure, in which of your Calendars to search.
This App needs the permission to access your Contacts, only because it needs to evaluate the available accounts. This is unfortunately the same permission group. The App will not actually read your Contacts.