If you want to critique evolution, you should leave off reading YEC apologists and start reading actual science. I know it’s hard for you to believe, but the Christians you trust to tell the truth regularly lie and twist facts to make the evidence fit their predetermined conclusions.
Otherwise known as the “fallacy of the beard” – how many hairs does it take to make a beard? Abraham tried to use this tactic on God to save Sodom in Genesis 18. Didn’t work.
If you want an actual answer, scientists have studied something called “minimum viable population,” which is how many individual adults are needed for a population in the wild to have a 90% survival rate after 40 generations. The best answer is around 7000.
I would absolutely not agree with that proposition. We have zero examples in history of that happening. New species arise from a population. Genetics 101.