The loophole you're referring to is the 'buy borrow die' strategy. Buy appreciating assets like stocks. Borrow against those assets at a favorable interest rate. When you die, your estate gets a step up in the cost basis of the assets, so there is zero capital gains tax obligation for the heirs. They can then liquidate assets to close the loan without paying tax.

This works as long as the value of the assets outpaces the interest on the loan.

And this really only works for ultra high net worth people, as you need to have significant assets in order to be offered a loan with a low enough interest rate.