Platform Events are a little confusing as the Custom Platform Events found in Salesforce under Platform Events ->Custom Events, are stored under the Custom object metadata type.
Your events will then show as separate Custom Objects in the comparison view.
Depending on how your event is setup you may also need to include a few other metadata types.
The full list of metadata types that relate to Platform Events is as follows.
Custom ObjectPlatform event subscriber configPlatform event channel memberPlatform event channelEvent relay configFlowApex Trigger
Once you have added the above metadata types you should be able to deploy all required changes.