There could be diminishing returns after a certain number of bipedal robots. 20 billion sounds like it would be overkill. 1 billion maybe, maybe not

https://www.businessinsider.in/tech/news/china-boldly-claims-it-has-a-plan-to-mass-produce-humanoid-robots-that-can-reshape-the-world-within-two-years/articleshow/105017260.cms#:~:text=China%20revealed%20ambitious%20plans%20to,would%20%22reshape%20the%20world.%22

China boldly claims it has a plan to mass produce humanoid robots that can 'reshape the world' within two years

China revealed its bold plans to mass produce "advanced-level" humanoid robots by 2025. The Ministry of Industry and Information Technology published a roadmap