The short answer is that Socialism does work, and continues to work, and that SocDem countries like the Nordics depend on heavy exploitation of the Global South to fund their safety nets and still see shrinking worker power (a process Marxists call imperialism).
The longer answer is that Marxists don't believe Socialism is better than Capitalism for any moral reason, but because they are Dialectical and Historical Materialists. They track where Capitalism is necessarily heading, ie free competition gives way to monopolist syndicates with internal planning, socializing themselves and making them ripe for public ownership and central planning.
Similarly, the PRC is a Socialist Market Economy. The model is described as a birdcage, the CPC allows markets to naturally develop but only along their guidelines, and increases ownership as competition creates these new monopolist syndicates. Socialism Developed China, Not Capitalism is a good article going over China's economic model. The CPC has the power it has as a Dictatorship of the Proletariat, it needs that power to maintain supremacy over their bourgeoisie. Communism is achieved by degree, not decree.
A good primer is Why do Marxists Fail to Bring the "Worker's Paradise?" an excellent article that goes over materialist examinations of AES states vs idealist examinations. Another good reference is Blackshirts and Reds. AES is by no means perfect, but it does and did work.
Lemmy.world absolutely isn't Leftist, it's overwhelmingly liberal and the mods are anti-Marxist, even defederating from Marxist instances. Lemmy.world is allowed to be a liberal instance, but pretending it's socialist is silly.