I love dumbphones and I used to carry one until ~2 years ago, but it's increasingly untenable due to whatsapp. Couldn't care less about anything else. (perhaps an alarm clock? but even the dumbest of dumbphones has that)
Not only Whatsapp. Banks in a number of countries are getting rid of passwords, SMS 2FA, or code cards for their online banking. Instead, you either have to use their phone app for online banking, or you have to use the phone app as the second factor for logging into online banking through the browser. A dumbphone won’t suffice.
some of the nokia feature phones have whatsapp, if that interests you.