Once you've entered your Exchange server credentials into your Admin console, your G Suite users will see the option to Refresh all in the Find a time feature of Google Calendar.Clicking Refresh all will prompt Google to query your Exchange server for the free/busy calendar data of all users invited to a particular event.
If Google realizes that one of the invited users is not a G Suite user, it will query the Exchange server for that user's calendar data.
Google queries your Exchange server whenever a Google Calendar user in your domain clicks Refresh all in the Find a time feature of Google Calendar.
However, you can also publish Free/Busy information online, and access Free/Busy information published elsewhere.
If not everyone you collaborate with publishes Free/Busy data, you can still use You can publish Calendar and Free/Busy information to a Web DAV server, FTP server, a remote machine through SSH or to any other web server with HTTP PUT support.
We have seen issues were data from an appointment can cause Free/Busy lookup issues.