Why does China, a socialist country, have mega corporations like Tencent and Bytedance? Are they collectively owned by syndicates or unions? If this is a transitionary phase to socialism, can we trust China to actually enforce Socialism after this stage ends?

The "capitalist roaders" won as Deng and his allies came into power. They were Marxist, but wanted to approach China's development very differently - by allowing markets, i.e. a form of market socialism - and doing two mutually-reinforcing things:

1. Seek (qualified) foreign investment and build up China's productive forces, which is to say, build up heavy industry, light industry, services, etc, the whole shebang.

2. Do this at the expense of their own exploitation at the hands of imperialism. Accept the exploited country arrangement, but on their terms. Create an export economy, but one of commodities not raw materials. Depress wages (to an extent), depress exchange rates.

This resulted in an entanglement as well, a defensive strategy against imperialists. It is not easy for, for example, the US to cut off China, because it exported most of its manufacturing base to China, and China took over most new manufacturing since.

There's plenty to criticize (carefully!) on this path, but one thing is for sure: China's model coincides with its continued existence, which is more than you can say of, for example, the USSR. It is also in a strong position, having developed massively and lifted a billion people out of poverty in the last few decades.

To go over your other questions:

• China's government owns or co-manages many companies, usually when they exceed a certain size. Some are co-ops, with government mandates. Many are also private companies operating in special economic zones, i.e. market zones. China will also heavily regulate many industries.

• The question of when something is Real Socialism (TM) should be fuzzier, imo. There are many different socialist projects taking different approaches to gaining and wielding the power of the working class and we should (critically) support all of them. China is going in a good direction and has a seemingly valid strategy.

Child Labor in factories: Myth or Fact? I have a Chinese friend who said he personally never worked as a child in China, but obviously if this was true not every single kid would have worked in a factory.

Generally a myth. It's a real, large, diverse country, but has made huge strides to create an education-filled childhood for its people.

Surveillance and Social Credit: are these myths, or are they true? Why would China go so far to implement these systems, surely it'd be far too costly and burdensome for whatever they'd gain from that.

Outdoor surveillance is no worse than London. It's a myth in that it's ridiculously exaggerated and not fairly compared to surveillance in the countries that make anti-China propaganda.

Internet surveillance is probably about the same as well, but China's government acts on it more often. Not a ton more, but they do look out for various claims/behaviors and will take action in some circumstances.

Social credit is largely a myth. It's basically the same as a credit score.

Uighur Muslim genocide: Is this true?

No. Liberals are doing an old trope of genocidal trivislization by putting this in the same category as the holocaust. Happy to go into a critical look of what's happening, but the dominant western narrative is inventive and exsggerative.