The instructions are almost the same as this guide:
You can get the solenoid here:
You can get the source code to my kbd8x firmware with solenoid enabled here, from my QMK fork:
Here is a video of the solenoid in action (keyboard not yet assembled):
I’ll do a build stream later where I assemble the keyboard with switches and stabs and everything and see how the solenoid sounds with it all put together. I’ll post a video of that too.