Hm. Maybe make it some extra weapon mastery perk instead of being a whole feat? I don't recall what it did specifically, other than letting you grab stuff up to 15 feet away.
Third Hand (2014)
You are an expert in combat with whips and can use it like an extension of your hand. You gain the following benefits:
You gain proficiency with whips.
You can grab an object within 10 feet of you as a bonus action with a successful DC 10 Dexterity check. The object must have an exposed portion that the whip can wrap around.
When you hit a creature with your whip, you can attempt to grapple the creature. The creature must make a Dexterity saving throw. On a failed save, the creature is grappled. The DC for both the saving throw and escaping the grapple is equal to 8 + your Dexterity modifier + your proficiency bonus. Until the grapple ends, you cannot use the whip on another target.
You can pull a creature grappled with your whip to within 5 feet of you by using 10 feet of movement.
You can go toward any of the 2024 feat styles with this:
The style above is closest to an origin feat. It has a few more benefits than normal, but nothing earth shattering.
As a fighting-style feat, you would probably only use the third and fourth bullet point so that it is streamlined like other fighting-style feats.
As a general feat, you could add a requirent for 13 Dexterity and a benefit of +1 to Dexterity (like the Crossbow Master feat).
I would change things a little bit to fit with the "things automatically happen when you hit a target" style of 2024.
Third Hand (2024) Origin Feat
You are an expert in combat with whips and can use it like an extension of your hand. You gain the following benefits:
You gain proficiency with whips.
You can grab an object within 10 feet of you as a bonus action with a successful DC 10 Dexterity check. The object must have an exposed portion that the whip can wrap around.
When you hit a creature with your whip, you can choose to grapple the creature. The DC for escaping the grapple is equal to 8 plus your Dexterity modifier and your proficiency bonus. Until the grapple ends, you cannot use the whip on another target.
You can pull a creature grappled with your whip to within 5 feet of you by using 10 feet of movement.