Microsoft is not making their own determination of who the state actor is and is just letting the three letter agencies' finger pointing fly with no evidence. There is however significant evidence indicating a country other than Russia in the FBI's Solarwinds report that contradicts the headlines if you read the body of the report.
Such as?
The narrative US = good, Russia = bad is true but only if you are in the US. In Russia you see the complete opposite.
Both US and Russian intelligence have lied in the past, it's part of their job.
For example, the intelligence agencies don't have the right to spy or attack their own population (as far as I know), but there is nothing that forbids them to ask an ally to do it and put the blame on someone else.
Russia denies doing it, and both US and Russia have interest into collecting this data, so starting from there, it's important to keep an open mind that the interactions between countries are not black & white.