Depending on your Outlook settings, when you create a new appointment/meeting, Outlook automatically creates a Teams/online meeting (as shown below) and provides the invitees with the option to "Join Online".
Not all meetings need to be Teams or online.
You can disable this option as follows:
In Outlook, click on the File option at the top left of the window.
Select Options
Click on Calendar
Scroll down to Calendar options
Ensure that the option to create online meetings is unticked as below:
If you don't have a tick box as highlighted above, you may have an Add Meeting Provider box next to the text instead. Click on it and then ensure that the option is unticked
Click OK on the Outlook Options window.