There are two files, a version that is .8mm thick and a version that is .6mm thick.
The .8mm version is almost silent, but the buttons are a little stiff.
The .6mm version has a soft audible click, but the buttons feel a bit better to press.
I prefer the .8mm version for my use case.
Printed at .1mm layer height.
The video on this Reddit post shows the .8mm version: Quieter SP Membranes : r/SBCGaming (reddit.com)
The author marked this model as their own original creation.