I think that quantum immortality may contain limitations. From the combinatorial point of view we can consider many variants of constructed buildings on the planet Earth, in one universe 1 m high, in another 100 m, in another 1km. But there will not be a universe with a building as high as the moon, because the material used to construct these buildings is not suitable for such heights and the lower part will simply crumble under the weight of the upper part. Life can also have limitations. And if we have never met an immortal man from the Middle Ages or the ancient world, perhaps it is not because of a small probability of such an event, but because of zero due to some environmental limitations that exist in any universe