Drew, thanks for your quick answer. We will try with your approach.
Another idea (inclusive useful for other cases in my application) is to use a collection that is not synchronized, like a local collection, but I suspect that will not work because the doc mention: "Your application can use either the remote service (which provides access to both MongoDB Mobile and Atlas) or the local service, but not both at the same time."...
Do you know if I can use a collection as local and other collection as remote on the same app?