I know I'm asking for a lot of trouble here, but I'll ask anyway.

I see that, out-of-box, Luckfox Lyra has support for a few DSI displays -- a few more than Raspberry Pi has (wink). However, I'm trying to use something physically smaller than 2.8". I have a few ST7789s lying around, and I know for ...

Sorry I missed the previous responses. You can muck around with the device tree and set the LED behavior "none" instead of disabling it entirely. I found in <sdk_loc>/kernel-6.1/arch/arm/boot/dts/rk3506-luckfox-lyra.dtsi, there's a section that says

leds: leds {
compatible = "gpio-leds";
work ...

To disable the LED using sysfs as suggested previously:
echo 'none' > /sys/devices/platform/leds/leds/work-led/trigger

There appear to be other modes of LED operation, i.e. caps lock/num lock/etc. The available options can be found by running:
cat /sys/devices/platform/leds/leds/work-led/trigger ...