Number 1 suspect unfortunately would be the US gov.
That’s the thing that makes cyberattacks so dangerous, countries can get into offensive cyber operations for a relatively small amount of money compared to a new Aircraft Carrier or Fighter Jet, you don’t need that many people, the attacks can be carried from anywhere and you have some degree of plausible deniability.
Recently here on FR, we’ve had threads about the moon landings being faked and 9/11 being an inside job, I’ve even had people tell me planes didn’t actually hit the WTC Towers, I don’t believe any of that.
The number of people needed to carry out a massive cyberattack is so small, it could easily be concealed and USA being on the top of the suspect list would not be surprising to me.