The FTC has not made its communications public for now. A source states that they both reiterate one specific argument vs the deal. No, it’s not Call of Duty this time.
Google and Nvidia contend that Microsoft will gain an unfair advantage in the fields of cloud gaming, game subscriptions, and mobile gaming. Nvidia does not directly oppose the deal per se but seems to be concerned about questions of equal and open access to video game titles.
Apparently, both companies shared information to support the FTC's claim that the acquisition of Activision Blizzard would provide Microsoft with an unfair advantage in the categories of cloud gaming, subscription service, and mobile gaming. However, NVIDIA's position is reportedly slightly different in that the company highlighted the need for equal and open access to all games rather than directly opposing the deal.
It sounds like NVIDIA is primarily trying to protect its GeForce NOW cloud gaming service (sporting a user base of 25 million), likely in fear that the availability of Activision Blizzard games on the cloud would be limited to Game Pass after the deal's closure. It should be noted, though, that Activision Blizzard games haven't been available on GeForce NOW ever since the cloud service left beta in February 2020, when the publisher requested their removal. At the time, NVIDIA claimed it was all a misunderstanding and hoped to get the publisher's highly popular titles back on GFN, but that never happened to this day. NVIDIA is likely trying to get Microsoft to budge on Game Pass titles availability on GeForce NOW.
The FTC sued to block the deal a month ago. Microsoft has since replied, and the first pre-trial hearing took place last week, although the actual hearing is scheduled for sometime in August. On the other hand, the UK's CMA and European Union equivalent regulator body are expected to share their conclusion in April.