Trying to get 5G connectivity while roaming in Canada

I recently purchased a Galaxy S24 (CAD version, model SM-S921W), upgrading from a Galaxy S8.  I tranferred my SIM card over.  When I'm roaming in Canada, I seem to be capped at 4G speeds.  I've tried manually connecting to all the different carriers in my area.  I have another phone that has a Rogers plan on it, which receives 5G connectivity without a problem.

I chatted with various AT&T reps, who stated that everything looks fine from their end to allow for 5G, including my SIM card.  I suppose it's possible that every major carrier in Canada caps AT&T roamers at 4G speeds, but that's not what I gather from looking at various forum posts.  I've been roaming in Canada for awhile now, and have never seen 5G speeds, so it doesn't seem to be a matter of the time of day I'm connecting.

I'd appreciate any tips or suggestions anyone may have.  My APN settings are below.  I tried to manually set the APN settings to the "ENHANCEDPHONE" settings located here: https://www.att.com/support/article/wireless/KM1062162/.  However, as others have noted elsewhere, changing the MNC to 410 prevents the settings from being saved.  

APN settings:

Name: ATT Nextgenphone

APN: nxtgenphone

MMSC: http://mmsc.mobile.att.net

MMS proxy: proxy.mobile.att.net

MMS port: 80

MCC: 310

MNC: 280

APN type: default, mms,supl,fota

APN protocol: IPv4/IPv6

APN roaming protocol: IPv4/IPv6