It draws attention and coverage to the issue. It forces people to listen. Protest has to be disruptive to the norm to achieve that, and there will always be people who don't like that. That's the point.
As I say, I don't think this one is effective or proportional given the lack of control someone in Russia has over the situation, but just saying "nothing should ever be damaged in protest" is, I think, naïve at best.
If Russia were a state with a reasonable guarantee of a fair legal process, I would argue a moral obligation to disruptive protest to end the war. If the UK (where I am) were to invade another country like this, I would hope for a general strike, and civil disobedience of all kinds, including vandalism. The fact that Russia has such a hard line against dissidence makes this obviously more morally difficult, although I greatly respect those that still choose to protest, I can't expect it of anyone.
People will disagree about how effective a thing is, and how justified it is. What the Russian state is doing is monstrous, and that increases the level of justified disruption to me. That doesn't mean this was justified—I feel it wasn't—but pretending that all "vandalism" is inherently never reasonable as protest is, in my view, wrong.