This looks to be a country specific issue and affecting phones from India.
Yes bro same problem...faced this today after updating the July update.....not detecting the network...infact the sim manager option only not opening....I contacted the Samsung service call center today...they told a few members of note 8 experienced the same this....they told it's a bug in a update from their side....they told to visit nearby service center they will help u with this....
After update mobile network is showing blank
No menu option to select mobile network also
Tried power off and restart, SIM reinserting, reset of network settings - nothing seems to work