3G phones are unfortunately no better choice than 2G phones, because the 3G networks of most operators will be not running much longer than their 2G networks. Here in Europe operators often even plan to shut down their 3G networks prior to their 2G networks.
Kyocera indeed seems to have some 4G "dumb" feature phones: https://www.kyoceramobile.com/phones/?filter=type:basic#
That's quite interesting. Thanks for the pointers.