If you have ever issued an red x on your network bars for cellular data and when you go to mobile network settings it’s all grey out i have solutions for you.
My dad is a taxi driver and he had this issue, and because of it his tablet couldn’t work because no mobile signal and he couldn’t get any jobs.
Simple type *#*#4636#*#*
and then fo to phone/tablet information scroll down to turn on radio enable and exit.
This fixes the issue, if going to airplane mode or rebooting device doesn’t work.