Will there be as many cheap workers as last couple decades pouring 100 years worth of US concrete in 3? No, hence why all the upfront build infra investment right now, while blue collar still somewhat plentiful and cheap. Meanwhile, tons of resources pouring into automation / humanoid robots, because at PRC scale, IMO can't really immigrate/migrant worker way out of issue. Not saying it's not possible, see meme of circle around Asia where 50% of humans live. There's likely still going to be a lot of accessible cheap bodies around if culture willing to tolerate it.
The broader picture is big % (like 30%+) of PRC workforce has been (and will be until they die) bluntly... net drag. There were always 100s of millions of farming households (functionally a jobs program) and informal workers spinning wheels doing shit all. All the labourers and workers pouring concrete and building factories were only ever fraction of PRC workforce. PRC losing the fraction that doesn't do much and replacing it with a smaller fraction that does a lot, and when aggregate # of workers that does a lot is 2x-3x more than peers (vs past where peers had orders of magnitude more skilled than PRC), then that's much better net position for future when competing on high tech / high value. Another added benefit of not having 100s of millions of excess mouth to feed and fuel and future PRC demographics is also going to enable strategic autarky like US. IMO PRC "finite" still too much. There are a lot of benefits to where PRC demographics is trending within our lifetimes. Of course if they don't figure out TFR in 30-40 years things will get real bad in 60-70 years, but that's time frame too distant to extrapolate.