Pierre-Antoine Donnet is a experimented journalist with significant knowledge and experience with China since ~1980 (he was not happy with the Tibet events around 1985 and was present physicaly here for the Agence France Presse, the primary main source of most mainstream french media - independant medias have their own investigations). He's been cited twice on mediapart (independant leftist journal very respected here) on the topic.

He says basically:

China population declined officially in 2022, and "it started before despite the official source" as part of the source of the problem
PIB growth lower than targets and historical values, as a symptome of vicious circle
Some talk about the CCP internal conflict

I guess he's the primary source, but I don't want to buy his book to give you a summary :D