When Hong Kong made a Covid check-in app mandatory at restaurants, friends Birdy and Bu — wary of government tracking — decided to avoid eateries entirely and go for picnics instead. The idea caught fire: their private social media picnic group has swelled from 50 in December to more than 6,000 members, as many look to avoid sharing data in a city where distrust of the Beijing-backed authorities runs deep. Instead of scanning QR codes at restaurants with the government’s “Leave Home Safe” app, they simply order takeaway and find spots to eat with friends. “I just don’t like being forced,” Bi…