The transit ban appears to be even more sweeping than some previous reports indicated…

https://news.yahoo.com/hong-kong-airport-bans-transit-063024841.html

“Hong Kong announced a ban on passengers from most of the world transiting its airport on Friday as China ramps up strict anti-virus travel measures ahead of the Winter Olympics.
The Chinese business hub ranks territories into categories based on how widespread their Covid-19 infections are, with 153 countries currently classified as Group A -- from which arrivals must spend 21 days in quarantine.
Hong Kong's airport, in normal times one of the world's busiest aviation hubs, said anyone who has spent time in the last three weeks in any of those 153 countries would be banned from transiting from Sunday.”