Blanch, peel, and chop (optional). Bring a large pot of water to a boil. Add the peaches and boil for 5 minutes. Transfer the peaches to a bowl of ice water and let them sit for a few minutes. Peel the peaches and chop them (discard the pits). If you choose not to blanch and peel the peaches, just chop them and discard the pits.
Load the pressure cooker. Add the chopped peaches, brown sugar, lemon juice, orange zest, cinnamon, and vanilla to an Instant Pot.
Cook. Seal the Instant Pot and cook the peaches on high pressure for 1 minute. Allow the pressure to release naturally.
Reduce. Remove the lid of the pressure cooker and set it to saute mode (on high). Saute until most of the liquid has evaporated from the peaches, stirring occasionally. This should take roughly 15 minutes.
Cool. Transfer the peach preserve to a mason jar and allow it to cool.
Chill. Once the preserve has cooled completely, seal the jar and store it in the fridge. While you can enjoy homemade peach preserve right away, it gets better if you let it chill overnight.
Notes
You do not need to chop up the peaches if you do not want to. It depends on the texture of the peach preserves that you like. Preserves tend to have larger chunks in them for a thick consistency.