In general, homemade jams are not thick like the store-bought ones. I have already shared mango jam, and I have tried fig jam in Instant Pot (yet to share the recipe), and they weren't runny like this cherry jam. So I did not use any cornstarch. As it cools, the jams thickened. But with cherry jam, as it was a bit runny and since we are not using pectin, I used cornstarch. It helped to set the jam nicely, and it was like a store-bought one but without pectin. You can try this jam without cornstarch and simmer for 20 minutes and let it cool. If you are OK with the consistency, then enjoy it like that. If not, add the cornstarch slurry and simmer again.