Thank you for the replies.
The person for whom I'm asking makes steel cut oats all the time in their rice cooker on a porridge setting. Whole groats take usually take at least twice as long to cook, and more resemble barley or rice, and actually makes a great rice substitute. On my stove it takes about 50 minutes for for rice-like al dente, and about 60 for a softer barley-like texture.
I specified the rice cooker as this is the only option that fits this person's lifestyle at the moment. No slow cooker, no instant pot ( no room), no presoak over night (can't commit to the time).
My wife and I have oatmeal for every breakfast, and if it's just our usual steel cut oats I make 4 cups once a week which fills two 2 quart Cambro containers that we keep in the fridge. I make it on top of the stove using a 3:1 boiling water to oats ratio. After I add the oats to the boiling water I stir it for a minute or two turn off the heat, and cover. I let it sit 3-4 hours till the pot is cooled down, and absorbed the water. At breakfast we add some extra water to in our bowls of oatmeal,stir, and microwave for 3 mins. Not quite as good as making it fresh everyday, but very close and so convenient. This method doesn't fit with how our friend's schedule actually works. He likes the whole groats, but it isn't that much better he will sacrifice the time to try and experiment with it.