I do know that coffee grounds have been used with great success in the compost heap and I’m sure if they were of a fine-enough grind they could be used much like pumice in soaps.
But then, I found this:
https://www.healthline.com/nutrition/uses-for-coffee-grounds#TOC_TITLE_HDR_18
There may even be chemistry to the grounds. I think coffee is slightly acidic. Might the grounds be useful in a cleanser?
I had the similar thought to use them as an abrasive component like pumice.
I wonder if they can be pressed together to make bricks?
There has to be something somewhere.