[layman51]

I have never heard of "left spacebar" before. Sounds very interesting. So there can be two different spacebars on your keyboard?

[leereeves]

Some ergonomic keyboards are split between to the two hands (usually attached, but not always) and have a spacebar key for each hand.

But I always thought both keys sent the same signal to the computer.

[volemo]

Yes, both keys send the same key code to the computer, however, pabloescobyte said they’re using ZMK, so the left/right space bar distinction is happening on the level of the keyboard controller.