Make sure the timer is set to 30 minutes (mine is automatically that).
Add the milk and let it slowly heat in the Instant Pot for 30 minutes. (Please, do not walk away from it if it is your first time. However, now I do not watch it anymore. I return when my pressure cooker beeps after 30 minutes and so far I have not had the milk overboil.)
After the 30 minutes add the salt and the acid and give the mixture a gentle stir.You will see the milk separate into curds (will become cheese) and yellowish whey (we will strain).Leave it to stand for ten minutes.
Using a fine mesh strainer, drain the whey. Let the curds sit over the strainer for about ten minutes.A lot of people use a cheesecloth but I did not find it necessary with a fine mesh strainer.
Your Ricotta cheese is now ready. Alternatively, if you want firmer texture (Paneer cheese), leave it to strain for longer, or, using a cheesecloth, wrap the curds and leave them under a heavy weight (like a cast iron pan) on a cutting board in the sink for an hour.