I'm not sure if this will help as I've not worked with mushrooms, but in general a bead-beating or other mechanical process helps with fungal extraction. I've routinely used the Zymo Research Bacterial/Fungal extraction kits with very good results.

Dear sir @ Heather B Miller, Thanks for your suggestion.

Macerate the mushroom mycelium using micro-pestle in extraction buffer. It gives good concentration of DNA then extracting without macerating and just incubating in extraction buffer. I hope this will help you.

Dear sir @ Toshinungla Ao , Thanks for your suggestion.