iPhone 7 stuck at 3G and changes from 4G to 3G always

I have tried different sims as i told you I’m not alone take a look at this link there are too many facing the same issue please do resolute on this issue i too did not have the issue before updating to 14.6 I’m using the same phone since a year but never encountered such an issue before till the recent update

please take a look on this link

https://www.reddit.com/r/ios/comments/ntwhrw/internet_connectivity_issues_after_update_to_ios/?utm_source=amp&utm_medium=&utm_content=comments_view_all

here is another link

https://discussions.apple.com/thread/252824492

heres if you need more witness

I’m from Sri Lanka and I am using Dialog that’s the network and I have two different Dialog sim and also the sim before it was the same issue the sim isn’t damaged I tried a different carrier called mobitel and it was the same issue

the behavior I have noticed it the signal bar drops to 2 or 1 bar and then turns up 3G with full signal bar while there is enough 4G signal at my area

here are some photos

There is no apple cafe here at Sri Lanka i guess apple is mostly into seeking new iPhones instead of caring for their customers who got old devices such as iPhone 7 most of my friends use to say this issue persists on iPhone 7 and 8 it seems like there is no solution

I did speak to them already what they said was they did come to our place measured the signal strength everything was fine they ran diagnostics not big work as wrong that’s that they said

The carrier said nothing wrong with the signal strength after coming to my place and checking running diagnostics they was at our place cause i made a complain