Though it’s unintuitive, the validity of a sample size has more to do with its literal value/size than how it compares to the total population.
If you have a sample size of 1000, your predictions about the 2000th individual in a population of 2000 will be just as accurate as your prediction about the 10,000,000th individual in a population of 10,000,000.
A bigger sample size is better, but it has almost nothing to do with the total population, it doesn’t matter if it’s 1.2 billion or 100 trillion.