I don’t know about China but in Russia, unless a man is in the military or has an active mobilization order he can leave Russia at any time, for any reason, without question (as long as he has a valid passport). For that matter any Russian citizen can return without question either (this came up during Covid where many countries weren’t even letting their nationals return). Russians are pretty sensitive about this and made sure it was very explicitly expressed in the Constitution (after everything that went on in the USSR with exit control).
That’s changed and men of an age eligible for the military are explicitly not allowed to leave. If they manage to bribe their way out, their families will receive a 5% tax - on top of any other taxes.