Yeah, the reintroduction of buffalo to America is the single most successful repopulation effort in history. Buffalo were nearly extinct in America. To start the reintroduction efforts, they had to buy a few breeding pairs from private owners who had captured them for their ranches. If I remember correctly, every buffalo in modern north America came from that group of only 3 bulls and 9 cows. And now the buffalo population has resurged to the point that they’re not even on the threatened list anymore. Their population will never reach the same point that it was at its peak (c.1700, there were an estimated 29 million buffalo in North America), but they’re at least not in danger of going extinct. They reproduce relatively quickly, and babies are likely to survive, so herds grow relatively quickly if left unmanaged.

The issue with buffalo burgers (and the reason they’re not in more restaurants) is that buffalo are hard to farm commercially. They make bad animal husbandry candidates, because they’re extremely territorial and get aggressive towards people. So farming them is something that needs to be done with a lot of caution, and buffalo farms likely won’t ever reach the same kinds of sizes as modern cattle farms.

Yeah farmed bison is certainly a specialty meat, but not a rare one. And yes, wild is an endangered species

Antelope Island in Salt Lake, Utah has a herd of bison that are carefully managed. There's a restaurant on the island as well that serves bison burgers.