It can be (locally) defeated. You can defeat it in wars of choosing, not in a war of annihilation (as Napoleon and others have learnt).

But in Crimea? Or the Russo-Japanese War? Or WW1? Whenever the stakes are less than existential, superpowers lose.

Saying Russia can't lose is just defeatism. With a few dozen F35s and better capabilities and ammunition, Ukraine would likely have won this war already.