Now the beauty of the Baryon mode is that it shaves the life of the person who they are fighting, so it was really helpful for Naruto in this situation as Ishikki didn’t have long to live.
Now Kurama only decided to use the Baryon Mode based on the Ishikki situation, where he was incompletely reincarnated which means he only had a few days or hours to live before he could plant another karma.
No, the mode is only shown in the manga so far which is way ahead of the anime. We won't be seeing that more very likely until about 2 or 3 years from now.
So basically Madara can’t be defeated with BM Naruto due to the battle situation.
In chapter #52 of the Boruto, Naruto get Baryon Mode. It is an ability that Naruto uses. To unlock the mode, Boruto uses one of his techniques on Naruto to give him a Tailed Beast Mode. Naruto eventually uses Baryon Mode to defeat Momoshiki and Kinshiki who were powerful enemies.
It’s in Naruto Shippuden episode #329 that Kurama becomes friends with Naruto. The episode covers chapters 570-572 of the Naruto manga.