Possible to use Process Builder subscribed to Platform Event to create New Record?

From docs:

If the process starts when a platform event message is received, associate the process with a platform event and an object, and specify matching conditions. Because every process acts on a Salesforce record, it requires a single record as a starting point. That way, the criteria and actions know where to start evaluating and executing.The process fails if it finds:

1) Multiple records that match the criteria.

2) No records that match the criteria.

This bit is bit funny from SF end, But you can bypass it, but providing a dummy record.

Create a dummy Object, with an external field `D_External__c'. Then create a single record of that dummy Object. And set Value of External Field as constant. eg 78234564654

Now add an extra field in your event My_External_Dummy_Field__C , and default its value as 78234564654 . The one you defined in the record you created.

This will make sure, each event fired will have My_External_Dummy_Field__C as 78234564654

In your Process Builder, Match your Dummy_Object's external field with My_External_Dummy_Field__C

As this matching condition will always match because of single record of dummy object and setting the default value of the platform event, your process builder will always run. And you can create do whatever you want.