Does the "Compass error, move aircraft or calibrate compass" error message that DJIG4 shows mean that the compass is being interfered with even though the map is accurate? Can the map be accurate, but the above error message will still appear?
As far as I can tell - not necessarily. Before the M2 I only saw it when there was magnetic interference, but with the M2 I see it every time I move more than 50 km or every 30 days - as expected based on the M2 firmware. And when it occurs for those reasons there is generally nothing interfering at all - the direction indicator is correct and the sensor compass interference values are all low in the green.
So yes - the compass and direction indication can be just fine if the message is triggered for that reason on a Mavic 2. Mine won't take off in that situation though - hence my earlier question about which aircraft you were referring to.
Another thought. Lets say an owner decides to always take off from the same spt and gets this error message every time. The drone allows him to take off, and within a foot of the ground. Lets further say that the message is due to magnetic interference. Is it possible that a long term consequence could be permanent damage to the compass?
I think it would take a very strong magnetic field to damage the magnetometers permanently, although they can become magnetized sufficiently to need demagnetization according to some reports.