Android 11 is Now available force LTE Only for 4G and NR only for 5G
Force 4G LTE Only 2020 is an App to Switch 4G or LTE only and going to testing setting page without secret code.

if you are in a weak LTE coverage area, You need to activate LTE only so it doesn't automatically change to 3G or 2G.

This app has 2 menu button :

1. SIM 1 Only : you need to using SIM 1 as default data connection.
2. Testing Setting as a shorcut to going testing setting page without secret code. Select Device Information to open Phone Info. Select LTE ONLY or NR Only to LOCK 5G

For Instruction : Tap menu at the right top side and select Insstruction.

Buy Pro version for Free ads and has new menu. it is Hidden Activity you can access from top right menu or Tap SIM 1 Only menu and then Tap Hidden Activity - Buy Pro Version

If activate LTE only and your mobile operators doest not support VoLTE (Voice over LTE), it will block to make going calls and receive calls.