Originally Posted by
TWA884
The difference is in the cellular bands. According to
TechWalls, in addition to the bands supported by the Canadian/Japanese version, the US version also supports the following bands: CDMA EV-DO Rev. A (800, 1900 MHz) and 5G NR mmWave (Bands n260, n261).
The CDMA capability will soon be irrelevant, as I don't think any carriers in the US or Canada will activate new CDMA service and are in the process of decommissioning their CDMA networks. Bands n260 and n261 are only used in the US, and only for mmWave service.
Also worth noting that the Canada/Japan version supports LTE bands 11 and 21, which are only used in Japan.
https://www.apple.com/iphone/cellular/#iphone-12-mini