Trying to find the name of a novel I read over ten years ago (I think?)
In it ancient Greek myths about science and magic were true as well as Chinese. The two were in a kind of space arms race to reach the “celestials”.
Potentially 'Celestial Matters' by Richard Garfinkle. Published 1996 so would fit with when you recall reading it. https://www.goodreads.com/book/show/1233406.Celestial_Matters
I've not read it, but the Goodreads description looks appropriate:
In this world, the Delian League (Greeks) and Middle Kingdom (Chinese) have been fighting a war for nearly a thousand years, ever since the time of Alexander the Great when the warrior-culture of Sparta and the Athenian Akademe were fused into a half-world conquering force. Their technologies are locked together, however, and neither empire can gain the upper hand. Each side secretly despairs of its chances and has come to consider desperate measures.