[AussieAndroid]

I cannot. I have no option to turn it off. I can enable wifi calling which turns it off, but I don't want to use that either.

Is there anyway to force the issue?

[claykin]

Carriers are going in the direction of packet switched calls (VoLTE). Eventually they plan to do away with their circuit switched network, so recent software updates and newer hardware seems to take that control out of our hands.

Maybe there's a service menu option to disable, but not sure.

[Rukbat]

Depending on your carrier, there may not be any circuit-switched phone connection any more. Talk to them and ask them how to turn VoLTE off on an S9 on their network.

[claykin]

Depending on your carrier, there may not be any circuit-switched phone connection any more. Talk to them and ask them how to turn VoLTE off on an S9 on their network.

I believe you mean VoLTE compatible phones, while connected to a VoLTE capable network, will not use circuit switching?

Circuit switching isn't going anywhere, yet. Even VoLTE compatible phones sometimes use circuit switching for calls. Not common, but they do. And they do everytime when connected to HSPA or less networks.