What are the present conditions (or restrictions) regarding professing Christians in Hong Kong?

As of 2016 there were 480,000 Protestants and 379,000 Catholics in Hong Kong. The quotes below, taken from a Wikipedia article, provide a useful overview of the relationship between the People’s Republic of China, and religion in China:

The People's Republic of China is an officially atheist state, which while having freedom of religion as a principle nominally enshrined with the laws and constitution of the country, nevertheless possesses a number of laws that restrict religious activities within China.

Banning discrimination against religious citizens in China is usually not interpreted to mean that positions in the government or military are equally open to believers in religions. Communist party membership is often a prerequisite for many government or military positions, and the communist party will frequently not allow religious believers to be members on account of their religious beliefs.

'Normal religious activities' is interpreted to mean religious activities carried out by religious bodies that have official government approval. Religions that are not permitted to exist in China like the Falun Gong or Jehovah's witnesses are not protected by the constitution. Religious groups that are not registered by the government, like Catholics who are part of an underground church or Protestant house churches, are not protected by the constitution. Furthermore, religious activities by approved groups that do not conform to the many regulations governing religion in China are also not protected by the constitution.

In 2021 the Chinese Communist Party passed a law called "Measures for the Administration of Religious Personnel" that Confucianism, Taoism, Buddhism, Islam and Christianity must be loyal and obey the Chinese Communist Party. Taiwan criticized that law slamming Chinese Communist Party regulating freedom of religion. https://en.wikipedia.org/wiki/Chinese_laws_regarding_religious_activities

This article is more specific:

After the transfer of sovereignty over Hong Kong to the China in 1997, governmental support from the Church of England was reduced. In China, the ruling Communist Party distrusts missions and humanitarian entities with international religious ties, like religious organizations with missionary connected objectives. China officially supports state atheism and views all religion including Christianity as subversive.

The government has in the past closed many churches and schools on the mainland and continues to practice religious persecution of minority religious groups. Since 2010, mainland China has gradually limited Hong Kong's Christian communities' ability to organize their churches in mainland China. Chinese officials have barred mainland residents from attending certain religious conferences in Hong Kong and sought increased oversight of mainland programs run by Hong Kong religious workers.

The Protestant community operates about 16 theological seminaries and Bible institutes, 16 publishing houses and 57 bookshops. They run seven hospitals, 18 clinics and 59 social service organisations, 74-day care centres, 17 children's homes, 35 homes for the elderly, 106 elderly centres, two schools for the blind and deaf, 47 training centres for the mentally handicapped and 15 camp sites. As in mainland China, Protestant churches in Hong Kong provide religious care to all who attend worship services. https://en.wikipedia.org/wiki/Religion_in_Hong_Kong

The extremely short Wikipedia partially quoted below refers to a white paper that reasserts China’s comprehensive jurisdiction over Hong Kong. Unfortunately, it says nothing about the impact on Christians living in Hong Kong:

"The high degree of autonomy of the HKSAR [Hong Kong Special Administrative Region] is not full autonomy, nor a decentralised power," it says. "It is the power to run local affairs as authorised by the central leadership." It also stresses that "loving the country is the basic principle for Hong Kong's administrators," who also have a responsibility to safeguard "the country's sovereignty, security and development interests and [to ensure] the long-term prosperity and stability of Hong Kong." It also asserts the necessity "to stay alert to the attempt of outside forces to use Hong Kong to interfere China's domestic affairs, and prevent and repel the attempt made by a very small number of people who act in collusion with outside forces to interfere with the implementation of 'one country, two systems' in Hong Kong."
https://en.wikipedia.org/wiki/The_Practice_of_the_%27One_Country,_Two_Systems%27_Policy_in_the_Hong_Kong_Special_Administrative_Region

China's comprehensive jurisdiction over Hong Kong means that its people are expected to respect and support the CCP. The two partial quotes below are from an article (8 July 2021) about the political and educational consequences of the national security law for Hong Kong citizens:

One year after the Chinese National People’s Congress (NPC) promulgated a national security law for Hong Kong, the political red lines established by the law and its implementation are clear. In essence, the people of Hong Kong must respect and support the Chinese Communist Party (CCP) and appreciate its contributions to both the socio-economic development of the People’s Republic of China (PRC) and to Hong Kong’s governing formula on the basis of “one country, two systems”. Those Hong Kong people who take action to seek to change the PRC’s political system are bound to encounter tremendous political risks and be accused of violating the national security law.

Hong Kong has changed drastically since the promulgation of the national security law in June 2020. China’s comprehensive jurisdiction over Hong Kong means that its people are expected to respect and support the CCP; that they should not do anything deemed to violate China’s national security and its developmental interests. Most importantly, the people of Hong Kong must be sensitive to the question of China’s sovereignty, meaning they should not assist foreign forces to intervene in the internal matters of the PRC.
https://asialink.unimelb.edu.au/insights/the-consequences-of-chinas-comprehensive-jurisdiction-over-hong-kong

Not surprisingly, it is extremely difficult to find reliable and accurate sources of information regarding events within Hong Kong. This is the best I could do within the time available to me. I hope it is useful.