Iacisrmma: Rabbi Avraham Blumenkrantz zatz”l originally made me aware of this through his Pesach sefer many years ago. Similar information is in this year’s edition, continued by his family. I have the App, and it lists information from the Badatz from 2000 not to use mushrooms on Pesach, with information from mushroom producers that it’s “grown” from rye or other grains in the compost.
This is why I prefaced my comment by unless something has changed, but in the absence of such data, I will continue not to use it. There may be heterim, but for me mushrooms are not a critical ingredient. As always, AYLOR, I just thought many might not even be aware this is an issue.