Well, we know that in many dictatorships support of the leader is marginal (e.g. just across the border - Belarus). This does not seem to be the case with Putin.
And yes, you can say you don't like the war in a poll. It's not North Korea.
Maybe you can see changes but you can’t see the actual number. The people being polled and the pollsters themselves are incentivized to lie.
They poisoned Navalny and then killed the doctor who treated him. If I am Russian living in Russia and I am asked by a stranger if I support Navalny, I don’t see any problem lying.
I doubt the average Russian is worried of receiving the same treatment that Navalny was given. The same way the average American isn't worried about being treated like Snowden or any other person labeled "enemy of the state".
And yes, you can say you don't like the war in a poll. It's not North Korea.