By Aditya Soni (Reuters) -Microsoft on Thursday briefly overtook Apple as the world’s most valuable company for the first time since 2021 after the iPhone maker’s shares made a weak start to the year on growing concerns over demand. Microsoft’s shares have risen sharply since last year, thanks to the early lead the company has taken in generative artificial intelligence through an investment in ChatGPT-maker OpenAI. Microsoft’s stock closed 0.5% higher, giving it a market valuation of $2.859 trillion. It rose as much as 2% during the session and the company was briefly worth $2.903 trillion. S…