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You are hitting the limitations of what Marketo can really do with SFDC activities (see Marketo / salesforce integration needs a serious overhaul, don't you "sync"? ). The type field is not available on Marketo side and cannot be used to filter.
So you need to get to a workaround, which is adding the information you are looking for to a field that is present, such as the activity subject. For this, you will need a SFDC workflow or process builder, indeed, but Marketo community is not the place to teach you how to do this (it is not a 2 minutes thing, BTW). Look at Salesforce Trailhead, there are a lot of resources there to help you.
Thank you Greg! This is very helpful information.