Hello
If you are using New Outlook, your Microsoft account needs to be using outlook.com or hotmail.com address/alias in order for this to work. Create an entry in the calendar and you will find the Teams meeting toggle to turn it on/off. Note, this is New Outlook, not Outlook Classic.
If you don't have an outlook.com alias, you can create one.
Sign in here: https://account.live.com
Go to Your Info > Sign in preference, Add an alias.
Create new: this will allow you to use the native domain outlook.com to create a new alias.
Once added, make this new alias your primary alias. Then you need to add this outlook.com address in New Outlook.