Suing over patent infringement has nothing to do with monopolies. This acquisition would be potentially very damaging to the industry, and Nvidia can make promises all it wants, but companies give assurances all the time to get mergers and buyouts approved then don't follow through.
NVIDIA secured an agreement to buy the often-essential chip-design company ARM for ~US$40 billion in late 2020. However, regulators are still scrutinizing it and its ramifications for the tech industry prior to approving it. Now, Qualcomm has sent an official notice of concern over the same with these bodies.