Perhaps you want to select what all Appointments should be synced to Outlook and not all from Dynamics 365. You can simply have a custom filter control this behavior for yourself and choose which all Appointments should go over.

Customization

Add a new Two Option field in your Dynamics 365 Appointment entity which will specify if the Appointment should be sent to Outlook or not.

Personal Settings

Now, you’ll need to add this field to the My Appointments view for yourself. You can do so by going into your Personal Settings from the Gear Icon on top-right corner

Then, go to Synchronization and select filters as shown below

You can modify the My Appointment view in your custom filters as follows

Choosing which Appointments to Sync

Now Appointment 1 and Appointment 3 are marked as Is Syned? == Yes. So only those will appear in the Outlook and the rest will stay in D365 itself.

Scenario

In my Dynamics, I created 3 Appointments – Appointment 1, Appointment 2 & Appointment 3.

Of which, Appointment 1 and Appointment 3 are marked to be synced and Appointment 2 is marked to not Sync. See below –

So, only Appointment 1 and Appointment 3 will be synced and not Appointment 2

Hope this helps!