SIA flights are operating but the loads are very low, mostly double digit numbers, but you can afford that when you have the level of government backing that they do. The idea seems to be to have the network maintained and ready for the recovery. The demand is certainly there, but regional rather than long haul is likely to bounce back first.
Most countries seem to have abandoned the zero COVID strategy, unfortunately HKG will have to go along with the mainland. The Chinese vaccine whilst having a similar level of protection against serious illness is far less effective in preventing someone from getting infected and adding to the number of cases.