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. if you tap device Information. it will bring it to menu 1 above.

If activate LTE only and your mobile operators doest not support VoLTE (Voice over LTE)

it will block Regular Voice call.