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.

I personally use a Moaan 7. Android and does everything i ask it (I just use FDroid apps though). But do bear in mind it doesnt seem to run apps in the background at all. Just whats onscreen. Battery life is extremely long (probably not unrelated)

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...)