I dont really think India will follow China that closely. China has a heavy handed government that can enforce whatever policy they want, while India is a free country that hasnt even been successful enforcing laws that other free countries do.
So, any changes in India's population have to be driven by socio-economic issues. The biggest of these is probably urbanization, but India is <40% urban even today. India's falling fertility rate without heavy urbanization is promising though, and I think it portends that India might go lower than predicted.
China’s fertility rate was already going down before the one-child policy was implemented. The TFR there hasn’t rebounded back to anywhere near replacement since the policy was repealed, due to socio-economic + cultural factors, COVID-19, and possibly the skewed sex ratio among under 40s. I would expect India’s fertility rate/population to be lower than current projections for similar reasons (including a male-heavy sex ratio).
