A soft launch, in celebrity and social-media terms, is the art of hinting at a new relationship without announcing it: a photo showing only a hand on the table, a foot at the edge of a holiday picture, or a whole person with the face conveniently hidden. Merriam-Webster now records the romantic sense, together with its opposite, the hard launch, an emphatic public declaration that two people are an item.
The phrase was borrowed from business. Companies have long soft-launched restaurants, websites and products, opening them first to a limited audience to build curiosity and fix problems before the full release. Applied to love, the logic is identical: test the reaction, read the comments and keep the option of quietly deleting the evidence. Followers, naturally, treat every cropped photo as a puzzle to be solved.