I believe the way that the program works is you can defer taxes from your original capital gains (and the cost basis gets increased so your deferred taxes are less than you would pay otherwise), reinvest them in an "opportunity zone", and not pay capital gains on your investment on the opportunity zone, if you hold it long enough
e.g. Bob bought Apple stock for $50 a share back in the day, and sells it for $200/share. He defers his taxes until 2026. Instead of paying capital gains tax on $150/share, the cost basis is adjusted by 15% so in addition to benefiting from the time value of money, future Bob will only be taxed on $142.50 of capital gains. Bob can buy a house in an "opportunity zone" (from scrolling around the embedded map, there's plenty of million dollar+ houses in these areas. There's also lots of sports teams and stadiums in these areas, so maybe Bob buys an NFL team or a parking lot next to their stadium), rent it out for 10 years, sell it, and not have to pay any capital gains tax on the appreciation. Definitely not a bad deal for him!
e.g. Bob bought Apple stock for $50 a share back in the day, and sells it for $200/share. He defers his taxes until 2026. Instead of paying capital gains tax on $150/share, the cost basis is adjusted by 15% so in addition to benefiting from the time value of money, future Bob will only be taxed on $142.50 of capital gains. Bob can buy a house in an "opportunity zone" (from scrolling around the embedded map, there's plenty of million dollar+ houses in these areas. There's also lots of sports teams and stadiums in these areas, so maybe Bob buys an NFL team or a parking lot next to their stadium), rent it out for 10 years, sell it, and not have to pay any capital gains tax on the appreciation. Definitely not a bad deal for him!