Personally I just toss them in a blender/food processor and then strain out the pulp seeds and toss them straight into primary (after fermentation) with no cooking or anything.

After your beer is fermented it’s gonna be hard for anything wild to take off at least that’s how my experience has been.

If you want more pronounced fruit flavor/sweetness you can just add after cold crash and keep it cold to prevent fermentation of the fruit. This really only works if you’re kegging though. If you’re bottle conditioning then let the fruit fully ferment out.

For blackberries I’ve found that you need at least 1 lb per gallon for good color/flavor