I've tried to avoid smartphones.
I've failed, so instead I've tried to make smartphones do less (I have a Moto G8 and iPhone SE2 but in both cases install as little as possible and definitely no socials or similar).
The reason I failed to avoid smartphones is that dumbphones don't do enough - they are missing a password manager and a 2FA app.
On smartphones I use BitWarden and Authy, but I'd consider any non-Android non-Apple non-Microsoft phone that had similar functionality. Until I can get into my online accounts with the help of my phone, that phone is incomplete, even though I want nothing else except 4G (for network compatibility), calls, SMS, and a local music player.
I recently got a Pocketbook HD, which is a small Linux-based eReader. You can run your own "apps" on it with a minimal amount of hackery (I use KOReader[1] for example). I've been thinking of trying to get some passport manager/2FA running on it as well.
It's got WiFi as well (which I never use), and bluetooth for music (which is pretty useful when reading in noisy trains etc.) Actually it would be pretty neat if it could do calls and SMS: it's larger than a phone, but I don't need to always carry a phone, and I usually carry my eReader if I'm away from the house for various things (e.g. when I went to IKEA today I carried it with me to have something to read during lunch).