There are a bunch of strategies here, but one people oft repeat is the "buy, borrow, die" approach. Where, they are kicking the can down the road, but the magic happens at the die step. When the borrower dies:

Your heirs inherit your stocks, with their cost basis reset to the current price. This means that they have zero appreciation of your purchase of $RIVN at $67, despite it being at $420. They can then sell the shares, to pay the loans, and not owe capital gains, because there are no gains. Additionally, at this step cash can be extracted for no gains as well if desired.

So you avoid taxes while alive by taking loans (not income), avoiding capital gains (never selling), and then gains evaporate through a stepped up basis. There are some exceptions here - estate taxes, etc with ways around them like trusts, but this is the general mechanism.

Its worth noting though, that its not ironclad. In a significant downturn you can be forced to liquidate and it will hurt (see the news on Musk right after X purchase). Additionally, while people talk about this as being super popular, realize that in practice people who take advantage of these strategies also still have millions in cash flow, so its not a true borrow only $0 tax lifestyle, they will use already taxed money to manage them as well.

Minor nitpick. The step up in basis actually happens when you die (not when your heirs receive the assets), and your estate has to pay off creditors before distributing assets. So the debt is paid off first, then your heirs get whatever is left over. Net result is the same though.

I'm familiar with this strategy but there's one thing about it that I don't understand: After death, the loans are an estate liability, right? Doesn't the estate need to be settled before heirs get their inheritance? If i had an outstanding $1MM loan, wouldn't the estate need to liquidate some of that $RIVN at the $67 basis in order to pay the loan? and then whatever $RIVN was left over would go to the heirs at a stepped-up basis?