The first rule of kremnology is that Russia always lies without a shame, as lies are usefull and they incur zero cost on the liar.
Russia invaded because they felt Ukraine was showing a bad example of slavic people becoming a democracy.
Also Russia has always had an affinity towards Ukrainian genocide. See Holodomor.
Also there is the narrative of lost colonial honor, Crimea, Catherine the great, and other idiotic pseudo-historical ramblings of a demented autocratic propagnada.