I was copying bracers of defence and adding the tough feat to it. Yet it won’t change the characters HP. I can work around this by manually adding the feat to the character. Any idea on what I’m missing for this to work correctly?

Adding feats through items isn't much of a thing.

I'd recommend to instead have the item grant the feat's effects and add a note that while using the item one cannot benefit from the corresponding feat.

That modifier only exists for variant humans. I don't think it functions if added to any homebrew that is not a race.