There are sooooo many exfil methods, including with air gapped systems that are off-network.

Not at all beyond the capabilities of any of the top ~9 or so best State actors.

Edit: To answer your question, very easily on the 20TB.

One crude method with a simple device in particular works well if you just clone the monitor data and then use HDMI and pass through. Then just cat dir in encrypted chunks to something like a USB key connected to the passthrough. 4TB USB keys are out there. A week of that gets you 20TB.

How many of those methods can realistically exfiltrate 20Tb of data? That's quite hard even for well funded actors.