I lived in Indonesia for 10 years & spent a lot of time in various villages of friends etc.
When I was in villages during wedding preparations & other community functions when the women got together to make food in massive quantities, one of the things they made from scratch was coconut milk, so I learned from them.
You remove the shell first obviously, then brown inner peel, then very finely grate fresh coconut into a large stainless steel bowl. Pour hot water over that & let it soak for a while til it's not too hot for the hands, then get in there with your hands & go to town, mashing & mashing it until the fats are extracted from the coconut. It takes about 15 minutes with 3 women & 6 hands
so I'd say give it a good 20 minutes mashing at least. You end up with coconut milk. It's a very simple process. Unfortunately, it is very difficult to find unadulterated coconut milk in a can, or otherwise. There used to be one brand that was nothing but coconut at a very night percentage & water, but the company went & added polysorbate 80 to it as a stabilizer / emulsifier, which ruined it. I used to use that brand but have stopped because of this.
I now do the coconut milk making by hand because of the problem of adulterated product, but when I am a little short on time, I will use my blender for the 'mashing' process. I still finely grate the coconut into a bowl first however, then pour the hot water over it & let it sit a good 30 minutes, til the water isn't scalding hot. I then put it in my blender & pulse the mixture for about 5 minutes or so, then let that sit til most of the coconut sinks to the bottom. I then pour everything into an unbleached cotton bag which I place over a strainer, strain it, then squeeze the
out of it. A thicker cotton is a good idea so the fabric doesn't split. You can find cotton drawstring bags like this on Amazon, sold in mutipacks.
If I have time, I then put that cotton bag full of coconut on a plate & put some serious weight on it to extract the remainder of the fats for several hours, then refrigerate / freeze until I need it. If not using within 24 hours, best to freeze it.
The majority of frozen coconut you'll find in Asian or other markets have sulfites added to the coconut, so read the label before buying. This additive commonly causes allergic reactions, which happened to my neighbour very recently. Lots of itching & hives. Not pleasant.
So yeah, that's THAT rabbit hole