Of all the materials that had me scratching my head in Grounded 2, lingonberries were one of the worst. You need lingonberry leather to get the Omni-Hammer II upgrade, so this sharp-tasting berry is quite the roadblock early on.
Similar to requiring blueberries for blueberry leather, lingonberries only spawn in very specific locations. If you've been following the main missions, then you might have been able to find one lingonberry already, as Signals and Stashes sends you to Pine Hill, where you can find a lone berry by the Milk Molar stash.
