Go to the play store & download Samsung Band Selection.
Click on.... Launch band selection
Top left corner click on the 3 lines by network
Click on Band selection
Scroll down to LTE B20 & click on it.
Top right hand corner hit the Selection button.
Now check your phone signal.
This works for me on EE.... You may need to experiment a bit on other carriers.
In my house I normally get 1 bar = 116 dBm By selecting Band 20 I can now get 4 bars = 85 dBm
Not sure how it will work for you but It's worth a try.
Try band LTE 3... I tried all the EE bands. Band LTE 3 in my house was best for 4g & band LTE 20 was best for phone signal.
Try these bands to see which is best for you..... Band LTE 1, LTE 3, LTE 7 & LTE 20
I did this as my phone keeps not connecting when people call me. Tried B20 signal went from -135 to -109, but if I try to call my phone it instantly disconnects. On EE. There is no 5g at my home address so only have 4g anyway.