SoftBank Group Corp. is in talks to acquire Graphcore Ltd., a struggling British semiconductor startup once valued at $2.8 billion, according to people familiar with the deals. The two companies have held discussions over several months but entered into more advanced deal talks recently, said the people, who asked not to be identified discussing private matters. Financial terms haven’t yet been decided and the talks could still unravel, they said. A final agreement isn’t imminent, one person sai...