When you sell real estate at a profit, you have to pay capital gains taxes on the profit. There is an exception to that in the tax code, called chapter 1031. If the proceeds from the sale of the property are held in a third party escrow account and not accessible to the parties involved, and the funds are used to purchase another investment property, the taxes are deferred.
Biden says that this amounts to an interest free loan from the government to the investor. It’s as if he thinks that this money belongs to the government and the only way you keep some of it is because you are somehow using a loophole, even though it is actually part of the tax code. Unless he gets is way, of course.
What Biden wants to do is eliminate that chapter of the tax code, thus forcing the seller to pay the capital gains taxes upon sale without the deferral that has been available for a century.