Are there two proposed bottlenecks, one at 900 kya and another at 70 kya? I'd only really heard about the latter.

The paper linked in that post proposes a bottleneck at 900Kya in the ancestors of all modern humans. There is a bottleneck associated with the migration out of Africa and the peopling of the world that many populations have, but not all. Based on genetic data the timing is between 100-50Kya, with a lot of the uncertainty coming from converting generation times to years (i.e. how many years on average between parents and offspring). This is a nice reference: https://sci-hub.se/https://www.nature.com/articles/nature213...