IDK, but i looked briefly a couple years ago and I wasn't happy.

Many of todays "dumb" phones run android just in a locked down mode where you can't install apps. There are a couple other OS options, I can't remember the names of those now. But they still had a full OS. Just running in a restricted mode.

To me dumbphone means just that. Dumb! No OS. Just enough h/w to connect to the cell network, like those HUGE oldschool cell phones in the 80's. Except small for pockets now. Once my dumbphone runs android, it opens up attack surface I don't want.

But I didn't spent too much time looking. So could be my seach skills failed me.