Can't select 3G on iPhone 13 running iOS 15

My carrier is refusing to make changes. You need to change the defaults so it works. Alternatively make the algorithm work better that switches between 4G and 3G. It chooses 4G when 3G behaves better with a stronger signal - this is Apple's fault not the carrier. Please fix it,, my old iPhone 6 is still better than my new iPhone 13 - this is not acceptable.

I see you have not replied. This one of those things where the customer is sitting in the middle of Apple and the Carrier with Apple saying it's the Carrier's fault and the Carrier saying its Apple's fault. That is not helpful for me the customer at all.

I think the way out of this is that you tell me what it is the Carrier needs to do to define the menu with the 3G option as well as the 5G, 5G Auto and 4G menu options. I think it's something to do the SIM although I could see it could also be the file that delivers the Carrier login details. Please tell me the tech details of what the carrier must do to implement the menu correctly and I will pass that info to my carrier.

I contacted my carrier and got this answer:

"If the Apple handset does not give you the option to select 3G this is an apple issue nothing to do with your giffgaff sim or 02. The best way to confirm this is a handset issue is to try the sim in another unlocked handset and trying to select 3G."

and yes, the same sim in my old phone has the options for 3G and 2G.

So this is the case of two groups each blaming the other. BUT its clear to me even if my carrier thinks its Apple and even if it's not then its Apples fault for lack of communication. I think this is a common problem with this new phone. I even heard Jim Cramer on CNBC complaining his wife's new phone does not support 3G.