actually brown rice flower isnt that nutritional for growing mushrooms.
It is widely used by beginers doing the pf tek method but most that are serious about it move onto using whole grains such as wild bird seed or rye and either coir , manure, or a compost designed for mushrooms.
Most that grow in brown rice flower add stuff like coffee for nitrogen and gypsum for calcium to achieve better results in fruiting
Mushrooms like a well balanced compost with many of the same nutrients that marijuana likes.
But different kinds of mushrooms thrive in different compost mixes and some wont even grow from it(like woodlovers).
So the mushrooms that people cultivate may not even like the same things as mycorrhizae.
Fungi in general are decomposers. Thats why there so great for plants cause they break down the soil into usable nutrients.
Fungi break down starches into glucose then feed off that so maybe its beter to focus on giving them starches to break down into glucose then glucose itself.
Im not saying not to try it though. Could be great.