Tiktok hasn't been banned and they didn't even block HK. They just want to keep their international and China operations completely separate (mainly to give the perception that China isn't interfering with Tiktok). The NSL makes it very clear that some Chinese laws apply in HK now which is inconvenient for a Chinese company who is trying to maintain a separate brand for non-Chinese territories.
Everyone is still free to use Douyin if they really must use Tiktok.