The best Warlock build in Diablo 4, for my money, is all about the abyss—a new shadow-based skill tag that's unique to their class. While these devil-pacted sorcerers can summon demons or hurl hellfire at enemies, their shadow builds absolutely shred, especially while levelling, thanks to one skill in particular: Dread Claws.
As someone who often plays shadow Necro myself, I could only look on in jealousy at some of the cool abyss skills the Warlock gets, including the best shadow-focused minion in the game through their Soul Shard mechanic.
The following build will, of course, contain spoilers for the Warlock skill tree, so if you'd prefer to experience and experiment yourself, leave now. Otherwise, here's the best Warlock build I've found in Diablo 4's Lord of Hatred expansion after 20 hours with the class.
Warlock key skills, passives, and Soul Shard
The Mastermind Shard you get from... 
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