Add the mixed berries, sugar, and lemon juice to your Instant Pot.
Allow to sit for 10 minutes. The sugar draws out the juices from the berries.
Place lid on Instant Pot and make sure valve is in sealing position.
Cook manual, high pressure, for 1 minute followed by a natural pressure release for 15 minutes.
Do a quick release if any pressure remains and once pin drops, remove lid.
Use a potato masher or immersion blender to smooth out the jam to desired texture.
In a small bowl, combine the water and cornstarch to create a slurry.
Stir slurry into the fruit mixture.
Turn the saute feature on and bring mixture to a full boil.
Allow to boil for a few minutes, stirring frequently, until mixture has thickened.
Turn off saute function and pour jam into containers.
Store in refrigerator for up to 3 weeks!