That's only a problem for those who demand exponential growth. And your assumptions are based on the unsustainable model of western imperialism; as China implements it's green energy, transport, automated agriculture, and housing policies, those sectors won't need to keep 'growing' as they do in capitalist states to prop up GDP. Even if it's right that if the slowing rate of growth leads to a net GDP shrinkage, it doesn't portend collapse.

That's not counting the effect of BRICS+ and the BRI on interpreting GDP. You don't need such a high GDP when you cooperate with your neighbours, when your GDP isn't a measure of how much you bully your neighbours and oppress your foreign and domestic workforce.

Many have repeatedly and outstandingly wrongly claimed either bluntly or in what they think is 'clever' subtleness that China is about to collapse. Do you really want to be in that crowd when the music stops?