The current consensus is that the minimum viable population for most species is between 500 to 1,000 individuals.
The problem isn’t inbreeding depression (you only need about 50 individuals to avoid that)—it’s lack of diversity to adapt to a changing environment. Pathogens would evolve that would wipe out the entire species because they’re too genetically homogeneous.
I saw an episode of Nova years ago where dna analysis showed as few as 70 people crossed the Bering land bridge and formed the basis of all Native Americans.
https://www.livescience.com/289-north-america-settled-70-people-study-concludes.html
That article’s over 20 years old—I’m not up on the latest findings, but I know there’s been major work since then on both the peopling of the Americas and on the importance of genetic diversity.