Coffee grinder or food processor will not work.

We've used something like this before: https://www.amazon.com/BI-DTOOL-Electric-Stainless-Pulverizer-Commercial/dp/B07W7PK7V6/

Cut the polypore into thin slices when harvested before drying.

Then dried thin slices into the grinder. The smaller the better.

It worked for reishi and chaga.