Mobile phones are not up to the challenge of tethering on a train. A device I would really love to have in my life but which AFAICT does not yet exist in a small/affordable enough form factor: a very portable USB-C 4G AND 5G dongle box with a chonky antenna (about the size of the antennae you get on fancy routers). With a little sucker to affix to a train window.
Anyone know of such a device? The glinet Puli AX comes really close to this functionality but... is not portable nor affordable.