Hello! If you've seen a small patch update go by, this is just a modification to set the internal dates correctly for this year's Halloween event on Steam (which will run from Oct 28th to Nov 4th).
During that time, the Pumpkinhead character should spawn on Hunting activities, allowing you to claim the Pumpkin Pie achievement.
But it won't be active until then this year so wait for it! (If you hunt and hunt and can't find a pumpkin *after* the 28th, let us know.)
In unrelated news Cute Bite is coming to consoles this Halloween! Got a friend who would enjoy an adorable vampire chomping on things? Look out for Cute Bite on Xbox, Switch, and PS4/5 web stores, it should be available on Oct 25th.