To help those of you out as to why the LTE dongle will not work on your
Mavic 3. Per the owner's manual that can be viewed on China's DJI's website. It requires a TDD-LTE Operating Frequency Band that US Cellular networks do not support.
It won't work in the US ever until DJI makes one that works with US cellular networks. The LTE dongle requires certain frequencies to work which US cellular infrastructure does not support. No network in the US supports the required frequencies.
I provided a photo of the manual for your viewing if you don't want to go to the website and check it out yourself. Places like Australia, South Korea, etc will support this frequency bandwidth. US Carriers do not.
Hopefully, this helps clear up any confusion.