@mirabilos
They do still make dumbphones. It takes a bit of looking, but they're there.

https://www.bestproducts.com/tech/electronics/g60343009/best-dumb-phones/ has a few examples (I have nothing to do with this site, just found it by a simple web search)
@scuttlebutt

@mirabilos @scuttlebutt The more modern ones do speak 4G. The difference between 4G and 5G is data bandwidth, which for a dumbphone is only relevant if you want to turn it into a mobile hotspot (but then you can buy a device specifically for that). For phone calls, a 4G dumbphone should be good for years to come.

Of course that doesn't answer the reliability, but then that's probably just another case of planned obsolescence, not much I can help with that...

@cks @scuttlebutt I don't think you're wrong, that's my experience too.