It is maddeningly impossible to get an ereader with all three of these features: b&w screen for maximum crispness; physical buttons for reliable page turns; modern processor for speed.

Boox Go 7 - B&W version.

It runs Android. It's a Chinese company and comes with a bunch of pre-installed apps, but I just blocked its abilities to phone home and use Koreader. It's been great for me

Boox Go 7 BW?

https://goodereader.com/blog/product/onyx-boox-go-7-bw "The Onyx Boox Go 7 is a dedicated e-book reader with a black and white e-paper display. This device has the same specifications and software as the Go 7 Color Gen 2, except that this model doesn’t have a Kaleido 3; instead, it uses the latest generation Carta 1300 e-paper panel, which increases responsiveness. The key selling points of this model are the physical page-turn buttons and Google Android 13, as well as full access to the Play Store. For those of you who want an e-reader that doesn’t lock you into a specific ecosystem, this deserves a look."

(slower by 2 minutes...)