Even setting up a vlan doesn’t work half the time because the mobile apps don’t talk directly with the appliance but phone home to a cloud service. A cloud service that will eventually go offline and leave the appliances orphaned. That’s how GE’s thermostats work.

Someone should make a service like this except you actually upload the file directly to the other user rather than uploading it to a 3rd party (encrypted or not). Yes I get you would have to wait for the user on the other end to connect to you before the transfer starts but if you’re uploading 100+GB of data you’re going to be leaving that browser tab open for awhile anyways.