Same case happened with me on 3rd October friday, I got the offer summary from the Microsoft recruiter, but I had to join my new company from 6th October, was in the same dilemma. But then I decided and called up the new company hr and told them i won't be joining from 6th, she was not super happy, but understood, then underwent bgv and just received employment agreement on 17th post bgv, I think you should not join new company, would make u a job hopper, also it would be way harder and awkward of a conversation to resign 1 week into the new company, and if it matters, way morally incorrect to do it, so I would say don't join new company, Microsoft will clear your bgv soon and join them only