China needs exports to Europe and the US. A nuclear war is not good for anyone

Russian nukes would be aimed at western countries.

China sells to western countries.

For one, because they gave Ukraine guarantees to that effect. You might also have noticed that Russia threatened the west plenty with nukes, but not Ukraine.

Noone really knows what the exact Chinese policy is there they like their strategic ambiguity but one thing’s for sure they are really big on non-proliferation, and thus aren’t exactly fans of nuclear blackmail.

I don’t think the Chinese would be triggered by Russia nuking its own territory, but then, well, Russia would be nuking its own territory. They could nuke Sudja to get rid of the incursion but they’d be nuking their own defence. Also, their own city. If they withdraw their defence first, Ukraine would gain even more territory and they’d have to nuke even more. Or, differently put: Just because the term “tactical nuke” exists doesn’t mean that nukes are sensible tactical weapons.

An exchange of nuclear weapons would be expected to ignite many fires and to spread dust and fallout into the atmosphere - similar to a large scale bush fire, volcanic eruption or a meteorite hit, depending on the size and number of weapons. This would have a chilling and darkening effect on the climate, causing crop failures worldwide. A world-wide nuclear winter effect would impact everyone, not just the parties to the conflict.

That’s why, for all the posturing and sabre rattling, even the most belligerent states don’t want a nuclear war - it means destruction of all sides, and massive casualties around the world.

There’s a big chance the West doesn’t just retaliates against Russia but at the same time launches to China and North Korea, so it’s in everyone’s best interest to not launch any nukes. You can imagine China getting a bit antsy every time Putin talks nukes in such a scenario.