The idea that China's real population might be lower than the officially stated 1.4 billion exists, but officials have not confirmed it
Independent experts and demographers do have suspicions for a number of years that the Chinese Communist Party (CCP) could be inflating its population numbers for various political reasons including for Chinese researchers to show strength attract investment maintain global influence etc.
In reality, the recent reports do show that China’s population already began to decline earlier than the time that the CCP admitted around 2022/2023

• The effects arising from the old one-child policy,
• The population's rapid aging process.
• Current birth rates can be seen as quite low.

Certain experts (like demographer Yi Fuxian) even suggest China's real population may now be closer to 1.2 billion or fewer.
Nonetheless, there isn't official, concrete evidence that the public statistics are false. Certain leaked CCP documents would be examples of official proof. Its basis mostly forms from indirect signs, demographic models, and analysis.

• A major demographic collapse hidden by China is quite possible.
• Indisputable evidence is what is needed to say so with complete certainty as yet.

Global economics, as well as geopolitics, and China’s internal stability would totally change it depends upon the veracity of that