(Bloomberg) — Nio Inc. retreated the most in nearly three weeks after unveiling the biggest U.S. fundraising plan by a Chinese firm since Didi Global Inc. Shares in the electric carmaker dropped as much as 6.3% Wednesday after it announced plans to sell up to $2 billion of American depositary shares, which would boost its cash holdings amid supply-chain disruptions and ahead of its planned Hong Kong listing. The company’s plan for an at-the-market offering adds to a banner year for such deals. Unlike traditional stock offerings that cater to institutional investors in one large transaction, these plans let companies…