If you can't update your firmwear over your internet connection or through the DJI Assistant 2 for Mavic download. Try doing it over a celluar network rather than your home internet. I know it's not ideal but it diffently works.(It's very slow!) I think that there may be some sort of firewall that is preventing the DJI downloads from working. Same goes for the andriod APK's; they will only download over celluar networks.

What version are you at ?   Is it your first time updating your smart controller ?    A Smart Controller with a firmware version of v01.00.04.75 or earlier must be updated using DJI Assistant 2. Download the latest DJI Assistant 2, and follow the steps in Firmware Update section in the DJI Smart Controller User Manual. Download DJI Assistant 2 at   https://www.dji.com/cn/mavic-2/info#downloads
You must also turn off your screen saver on smart controller until update is done.   Contact DJI Support if the update fails several times.