The Associated Press had this information. Here is an excerpt:

The Hong Kong stock exchange halted trading of Next Digital shares Monday at the media company’s request after authorities froze assets belonging to its founder, Jimmy Lai, who has been a high-profile voice in the the territory’s pro-democracy movement.

Later in the day, the media tycoon and nine other pro-democracy activists pleaded guilty to taking part in an unlawful assembly in 2019. Lai is already serving a 14-month sentence for his role in two other unauthorized assemblies during a period when Hong Kong residents were involved in mass anti-government protests.

Next Digital said in a filing that it requested the trading halt after authorities announced the freeze on Lai’s assets Friday under a national security law that critics say is meant to snuff out dissent in the semi-autonomous Chinese territory. Next Digital publishes pro-democracy tabloid Apple Daily, and the company was founded by Lai, who owns a 71% stake and is its controlling shareholder.

Here’s the link to the full article.