I doubt China will make a direct military move against Russia ever. That's not how they invade their neighbors.

Instead what they like to do is arrange some kind of development contract, usually mining or something similar, where they take over a large piece of land and then basically have free reign to bring in whatever equipment and personnel they want and extract resources with little oversight, few if any environmental regulations, and no labor laws. They will either import their own workers who will basically be treated like slaves, or hire local workers if they're cheap and treat them the same. Also it's pretty easy to import some surveillance equipment and a few PRC enforcers amidst all the industrial gear and specialist personnel.

For example:

• https://www.mining-technology.com/features/arrests-and-attacks-tracking-chinas-illegal-mining-in-african-countries/
• https://www.spglobal.com/en/research-insights/special-reports/china-s-global-reach-grows-behind-critical-minerals
• https://thediplomat.com/2024/03/canadian-miners-needs-capital-but-only-china-is-stepping-up/

Internally, China is starting to enforce stricter environmental protections:

https://www.sciencedirect.com/science/article/abs/pii/S2214790X23000096

Because of things like the damage that's been done to the Yangtze River and Poyang Lake:

https://www.asiafinancial.com/china-bans-sand-mining-on-yangtze-river

https://www.reuters.com/business/environment/reuters-graphic-devoured-how-sand-mining-devastated-chinas-largest-freshwater-2021-07-19/

So basically they're exporting environmental damage to other countries:

https://coastalcare.org/2018/10/chinas-search-for-sand-is-destroying-mozambiques-pristine-beaches/

(which is not really different from what western nations have been doing since the industrial revolution, it's just that in the present we know a lot more about the long-term impacts of the damage and the climate crisis is a lot more immediate, plus modern technology accelerates and amplifies the damage, and China is very aggressive in this area)

Russia is experiencing a labor shortage and will continue to for a long time after this war. I expect we will start to see deals with China to do resource extraction inside Russia, and once they're in it's very difficult to get them out.

tl;dr: military operations are expensive in terms of finance, politics, and international influence, but resource extraction deals are lucrative and develop soft power