There’s nothing complicated about the latest tobacco product trending online: Zyn is a tiny pouch filled with nicotine and flavouring. But it has stoked a debate among politicians, parents and pundits that reflects an increasingly complex landscape in which Big Tobacco companies aggressively push alternative products while experts wrestle with their potential benefits and risks. Zyn comes in flavours like mint, coffee and citrus, and Philip Morris International markets it to adult tobacco users. But videos of young people popping the pouches have racked up millions of views on TikTok and other…