There's different frontiers. Good farmland used to be the big thing. And trade routes, like natural harbors or navigable rivers. So in many parts of the world, most of the best places were already taken and the "frontier" was worse land. But not so in Americas, because there was available land for reasons. You could have "fertile frontier".

Over time when farming technology improved, people could live self-sufficiently in worse places. Transportation technology changed as well. Railways, highways. And now remote working and data centers. So there have been frontiers also in the old world in that sense. The king of Sweden in the 1500s declared some eastern frontier areas as tax free for some time, as he wanted people to settle there to control those areas (in accords, some of it might have been Russia...). Many places have waxed and waned over the centuries. When Estonia gained independence for the second time, some Finnish farmers went there as there was excellent farmland that was very underutilized.

With modern knowledge you could even build up a great place to live almost anywhere. Good policies and cheap energy. Maybe fresh water is the hardest physical requirement.