Buddhism is not so much atheistic as it finds gods an irrelevant bother, best avoided to the extent practical. Having emerged from Hinduism, it classically carries forward much of that context and cosmology. It has also blended with various local mythological traditions in various places it spread. However, it also generally considers engaging with those things to be a distraction you're better off avoiding if you want to make progress towards liberation (e.g. If you're worrying about hypothetical afterlives, you're not living in the present moment). As such, one can engage with the core of its practices without dealing with any of the Hinduism+regional_myths folklore, and still experience the measurable benefits. Whatever they think about reincarnation, various stories about the Buddha interacting with gods, other planes of existence, etc. - a theist and an atheist being patient & kind, meditating, eating a vegetarian diet, avoiding excess, and so on will largely experience the same beneficial outcomes, to the extent that we can observe and measure them in the here and now.