> I don't understand why the SEC (america) has jurisdiction to 'block' Telegram's operations (legal domicile in London)
Because Telegram “committed to flood the U.S. capital markets with billions of Grams by October 31, 2019” and “sold more than 1 billion Grams to 39 U.S. Purchasers, raising $424.5 million from the U.S. market” [1].
