Place the chicken feet and necks on a baking sheet or in a roasting pan. Place the sheet or pan on the middle rack of a 425°F preheated oven.
Roast feet and necks until they turn a golden brown. This can take approximately 30 minutes. If you want to accelerate this process, you can put the feet and necks under the oven broiler, but be sure to watch them closely.
Once the feet and necks have browned nicely, remove them from the oven and transfer them into the liner of the Instant Pot.
Deglaze the baking sheet or roasting pan with water and scrape up all the fond. (The "fond" are those browned bits that form on the baking sheet or roasting pan as the feet and necks browned.)
Add the water from the deglazing to the Instant Pot liner.
Add the vinegar and additional water to the Instant Pot liner to make sure that the feet and necks are covered with water. Don't worry if the feet float to the top of the water.
Allow the feet and necks to soak for one hour. Make sure that the Instant Pot is NOT on.
After one hour, add the vegetable scraps or vegetables to the Instant Pot liner. Add additional water to make sure that the vegetables are covered in water, but DO NOT use more water than you need. Use just enough water to cover the contents but no more. And never fill the Instant Pot liner beyond the pressure line. (See video.)
Place the lid on the Instant Pot and lock it into place.
Set the pressure knob on the lid of the Instant Pot to Sealing.
On the control panel of the Instant Pot, choose the Pressure Cook setting.
While still working with the control panel, set the temperature to low and the time to two hours. (See Video.)
The Instant Pot will click on automatically and begin building up pressure.
When the Instant Pot finishes simmering the bone broth, it will beep and switch over to a keep warm setting. At this point, you can manually release the pressure by moving the pressure knob from Sealing to Venting. BE CAREFUL. The pressure knob will release a forceful burst of steam. (Optionally, you can allow the Instant Pot to come down from pressure naturally.)
Once the pressure has been released, unlock the lid. Again, be careful as additional steam may also rush forth from the Instant Pot.
Remove the feet, necks, and vegetables from the Instant Pot.
Carefully pour the broth into a tempered half-gallon or quart-sized jar.
Fill additional tempered jars until all the broth has been removed from the Instant Pot liner.
Any debris you were not able to remove from the broth will sink to the bottom of the jar, and the fat will rise to the top and congeal once refrigerated. This fat will create a "fat cap" in your container that will keep your bone broth fresh in the refrigerator for 2 weeks.
If you remove the fat from your bone broth before refrigerating it, or if you break the fat cap, your bone broth will stay fresh in the refrigerator for one week.
Using an appropriate freezer-proof container, you can freeze your bone broth for up to one year.