I got the new ST7789 display with the microSD drive working! It was roughly the same code as the SSD1327 with the same pin assignments, including setting -1 for the reset pin.

https://www.adafruit.com/product/3787

One odd bit was that the display has much more resolution than the previous one. Since my display shows up on 1/4 of the screen, I'd say the resolution is 4 times as dense, but I could be wrong.

It's been slow making progress, mostly since I have other side projects that I am pursuing, but I did at least migrate over to the new display. This sets up using the microSD for memory storage later.

One tricky bit will be keeping time going with the watch while not connected.

My first thought was "OK, we need a small battery to keep the time ticking", but perhaps we can use a very small bit of power from a battery to keep things running, even if the watch itself doesn't have enough battery power to run.

Lots of stuff to do, but should be fairly simple to do each one.