I still primarily use an iPhone SE, but every couple of months I'll "disconnect" by using a dumbphone for a week or two at a time. I use the Nokia 106: https://www.nokia.com/phones/en_int/nokia-106/

I like it a lot. It's cheap, simple, and has great battery life; I charge it perhaps once during the week or so I'm using it. I paid £18 for mine unlocked.

My favourite antifeature is that it has no camera. Most dumbphones have a camera in them that's so poor it's not worth having. This one doesn't bother with one at all, which means there's no camera option cluttering up the menus.