In addition to whst @taanegl already said:

Hong Kong’s Freedoms: What China Promised and How It’s Cracking Down

Before the British government handed over Hong Kong in 1997, China agreed to allow the region considerable political autonomy for fifty years under a framework known as “one country, two systems.”

In recent years, Beijing has cracked down on Hong Kong’s freedoms, stoking mass protests in the city and drawing international criticism.

Beijing imposed a national security law in 2020 that gave it broad new powers to punish critics and silence dissenters, which has fundamentally altered life for Hong Kongers.

Beijing had been chipping away at Hong Kong’s freedoms since the handover, experts say. Over the years, its attempts to impose more control over the city have sparked mass protests, which have in turn led the Chinese government to crack down further.

In the years following the 2014 protests, Beijing and the Hong Kong government stepped up efforts to rein in dissent, including by prosecuting protest leaders, expelling several new legislators, and increasing media censorship.

Yes, there is strong evidence for these practices. Safeguard Defenders, a rights group, published a comprehensive reports on that issues, for example on China’s Consular Volunteers (November 2023):

For at least a decade, PRC Embassies and Consulates have been running consular volunteers in countries around the world. These have been seemingly undeclared to most host nations.

[…]

The network runs through United Front-linked associations and individuals and shows the involvement of the Overseas Chinese Affairs Office (OCAO), on which a January 2022 Federal Canadian Court decision upheld labeling as an entity that engages in espionage and acts contrary to Canada’s interests with concerns over “OCAO’s interactions with the overseas Chinese communities, the information gathered, and the intended use of the gathered information”.

Everyone interested can find more at https://safeguarddefenders.com and across the web.

Yes, but not only in Africa. There’s a comprehensive report by Safeguard Defenders from 2022, but you’ll find more, just search for something like ‘chinese illegal police stations’ as already suggested.

Just two examples:

China responsible for ‘serious human rights violations’ in Xinjiang province: UN human rights report

A long-awaited report by the Office of the UN High Commissioner for Human Rights (OHCHR) into what China refers to as the Xinjiang Uyghur Autonomous Region (XUAR) has concluded that “serious human rights violations” against the Uyghur and “other predominantly Muslim communities” have been committed.

Rights experts warn against forced separation of Uyghur children in China

Forced separations and language policies for Uyghur and other minority Muslim children at State-run boarding schools in China’s Xinjiang region carry the risk of forced assimilation, three UN independent human rights experts said on Tuesday.

What is a source you trust when it comes to China?

The report cites Latvia’s public broadcaster LSM, but you’ll find a lot of other sources (although at least some of them refer to LSM, too, or other media sources).

Charter97 is a Belarusian rights organization calling for democratic reforms in the country.