The only portable keyboard that I enjoyed using is the Think Outside keyboard [1]. It is a great compromise between portability and usability. But a lot of shortcuts are not working on moderne devices. It even works as a stand for the phone. But it uses 2 AAA batteries. I wonder if it would be possible to flash it to work with modern devices or even better, customize it.

[1] https://jsyang.ca/hardware/think-outside-bluetooth-folding-k...