Q: "I have been following the situation in Ukraine since 2014, but not too closely. I have been following very closely since the end of February 2022. Because of the latter, I think I know the general trends related to the development of SMO since it started. However, what I missed was the year before SMO, i.e., since let' say early 2021 .. "
...
A: " ... Russia likely took all these build ups and provocations very seriously, and saw the writing on the wall that if it didn’t ‘cure’ the Ukrainian sickness once and for all, it would only escalate until Russia was totally surrounded by NATO aggression.

But guess what? The West only continued to escalate. In November (2021) the U.S. brought warships into the Black Sea.
It was a clear show of force and attempt to intimidate Russia. Given all the endless escalations from the Ukrainian side in Donbass, and the increasing rhetoric and ‘shows of force’ of NATO in the Black Sea and elsewhere, Russia began to see the writing on the wall and, as I said before, likely decided that the conflict had to be ended once and for all.

Of course Russia still refused to be the one to pull the trigger first, so after a force build up, they waited. It is then well known that Ukraine began massively shelling Donbass in January and February 2022, as recorded by the OSCE:

And as they say, the rest is history."