That's what, 3 people reporting the same actual issue (working in some places, not in others)? The others just mention general trouble calibrating around their place.
There are tens of thousands of Mavic Airs around, and you bet there are more than a handful travelling with them (I have).
Anyway even if you think it can be fixed by firmware that would require DJI to be aware of it through support channels, so you need to contact support. Unless they get a fre dozens of hundreds of reports they will never see that as an issue but just a defect on individual units.
Actually there's a new firmware coming out today, so you could try that - but there is no mention of anything compass related in the changes.
Funny that in this thread someone said they contacted support and response was they should replace it, and another one said that demagnetizing helped (both points I raised last night).