You only get a recall (e.g. the one you mention) done for free.
However, if you have a problem with the existing software and an update would fix it then you can get that update done under warranty.
I got an infotainment upgrade under warranty because the radio would sometimes get stuck and refuse to respond until the car was turned off.
If you have any problems with the software let them know as there might be an update that can be done under warranty that would fix it.
I understand why the dealers don't just do updates - it will cost them to do so unless they can get MG to pay them for it as a warranty claim.