Each time I've been to the US recently my phone (iPhone SE 2022) has been unable to get onto any available 4G network. This is despite all the settings being correct and 3 telling me it should be fine. Other people seem to have no problems. I can get WiFi without any problems.
Is it best to simply get a US sim card when I arrive, or is there another option I can set up before I go that I haven't thought about?