Screen concerns

Is the screen reflective, transflective, or refractive?
I'm a big fan of electrophoretic (e-ink) screens because they work great outside, which is where I like to be.
From the very little I've heard, Bangle.js doesn't work great in bright sun.

Can I replace the screen with eink (I already have a screen from WaveShare I hope I can use)?
What interface does the screen use (the hardware documentation is woefully sparse)?

No idea if it is technically possible.
But I just thought about refresh time and life of the screen.
The firmware and all apps are not made for e-ink displays. This might lead to too many refreshs and bad readability and a shirt life of the screen.

Did you see https://www.espruino.com/Bangle.js and https://www.espruino.com/Bangle.js+Technical ? There's a bit more in depth info there.

The screen is a 240x240 IPS LCD with a ST7789 driver used in 8 bit parallel mode. It's a pretty standard backlit job used in the majority of these kinds of watches.

It connects to the PCB via a pretty fine pitch connector. I think realistically the chances of adding your own screen are extremely low. You could design your own little flex PCB adaptor for your new display, then create your own firmware that used the new display's controller, but I think realistically it's unlikely anyone would bother with that.

Thanks Gordon, but the alternative is building myself an entire smartwatch from the ground up, wouldn't you think that was even harder? I'm beginning the slow process by looking for a chip on which to base it.
If there is a hardware-hackable smartwatch that already has a reflective or transflective screen that I should be modifying instead, please let me know.

There is e.g. DK08 and SMA-Q2, both ~$30 on aliexpress, both hackable in a sense that you can upload your firmware (e.g. Espruino) without taking device apart. For Q2 see also https://hackaday.com/2020/01/30/sma-q2-smart-watch-is-completely-hackable/ As for DK08, I have one that I bricked, second that I gave to someone and waiting for third to arrive.

However those are otherwise quite limited when compared to bangle, no gps, compass, no touch screen, dk08 has just one touch button and that's all.

EDIT: also there is another strange one called CV16 (see e.g. here ) that should be hackable too (DaFit type firmware like P8) but figuring out how to update both displays could be a bit tricky.