Your iPhone 13's 5G signal may not be fast enough yet. How to turn it off and use 4G instead - CNET
How To Use 5G On the iPhone 13 & 13 Pro Max - How to Enable or Disable 5G & LTE - YouTube
Is it bad to have the iPhone 13's mmWave window covered up with a case? Does holding it reduce signal strength for the high capacity 5G? : r/iphonehelp