Place all ingredients into the Instant Pot.
Seal on the lid. Set on manual for 30 minutes. Because the vegetable scraps are probably still frozen and there is quite a bit of water in the pot, it will take a while to come to pressure.
Let the pressure naturally release after the 30 minutes.
You can definitely make this on the stovetop if you don't have a pressure cooker. Bring to a boil, then simmer on low for an hour (or longer, for a stronger tasting stock). Then follow instructions as below.
Once the pot is cool enough to handle, carefully strain the stock through a fine mesh strainer. Strain again through cheesecloth.
Transfer to sealable containers and refrigerate if you're not using right away. Use within a few days or freeze.