If the reasons for a "dumbphone" are smaller size, longer battery life, decreased media consumption, and increased privacy – then such a tiny smartphone as Xperia XZ1 Compact[1] with AOSP ROM without Google provided by Sony[2] would still cut the mark.

[1] https://www.sonymobile.com/global-en/products/phones/xperia-...

[2] https://developer.sony.com/file/download/software-binaries-f...