Google Meet only works with G Suite / GMail accounts. So, if you have a G Suite or GMail account, it's really simple to automatically add Google Meet web conferencing to meetings scheduled with FreeBusy.
Go to Calendars and Integrations.
Click on Integrations tab and Link Another Integration.
Find Google Meet and click Add.
Your Google Meet web conferencing provider will be automatically linked to your FreeBusy account.
Then refer to this guide on how to select your default conferencing provider for meetings scheduled with FreeBusy.