The Mighty Silverfist is found in the Jungle Ruins map in Act 3, near the center of the map ... complete the Slithering Dead side quest in Path of Exile 2, including which reward you should ...
Certain Maps in Path of Exile 2 have poor layouts ... it's likely a more immediate change from the end of Act 3 on Cruel difficulty to Path of Exile 2's Atlas, but it can still be daunting ...