AFAIK Microsoft didn't put any kind of liquid money into OpenAI, it's something like "you can use up to nB USD of our resources for free", not sure how that should go into accounting. It could even be a liability without much juggling.
A while back there was a big fuss because executives were caught not paying tax on the fair market value of extra perks they were getting like use of the corporate jet on the weekends for trips to the beach house. Anything that’s not purely a business expense is considered compensation and is taxable.