Wash and pit the cornelian cherries. Finely chop the onion and crush the garlic.
Either in a pan or with Instant Pot set to SAUTE, heat 1 tbsp oil. Sweat the onion for 8–10 minutes until translucent. Add garlic and cook 1 minute.
Stir in smoked paprika and bloom for 30 seconds.
Transfer onion mixture to the slow cooker. Add cornelian cherries, ketchup, vinegar, maple syrup, mustard, Worcestershire, black pepper, salt, and chili flakes. Stir well.
Switch Instant Pot to SLOW setting. Cover and cook on LOW for 4–5 hours (or HIGH for 2–3 hours), until cherries soften and flavours meld. Keep valve closed to avoid losing moisture.
Optional Step* Blend smooth with a stick blender. Strain if you want a silky finish.
Taste and adjust seasoning — add more maple for sweetness, vinegar for tang, or chili for heat. If it is too thick, add a little water to get desired consistency.
Cool and pour into a sterilised jar.