I recently went to the states and was not able to use cellular data even though I purchased a us data plan. In my research, it was suggested by public mobile to change the cellular data APN. I followed the instructions but on my phone I am not able to manually change the APN for cellular data. I only have the option to change the APN for the hotspot. Any help would be appreciated. Thanks
It is normally not necessary to change the APN. I wonder if your phone was somehow connecting to Verizon. I remember seeing a report from someone saying their iphone did. How that's possible anyway I don't know but so they said. Your phone needed to connect to either T-Mobile or AT&T and to be set to 4G LTE. Other people seem to be saying that AT&T doesn't work for 5G but does for 4G. T-Mobile will work for either. But it's a moot point now as you seem to be saying you're back.
Go to Settings, cellular data network. APN should be isp.mb.com although it says sp.mb.com mine seems to work OK. Try both.