I do not really know how reliable this website is, but for example it says that my phone that I use on AT&T system in USA will not work on 4G LTE in France, but would work on 2G or 3G. That said, networks are deleting 2G and 3G capability.
https://www.frequencycheck.com/
It was a lot simpler figuring this stuff out when there were only 2G and 3G, then it was just a question of frequencies, but has gotten more complicated.
https://www.worldtimezone.com/4g.html