Do you mean the Russian opposition who are actually opposed to Putin and persecuted out of the country / existence, or the opposition Putin allows to exist to make elections appear legitimate? One of those doesn't support the war, and one of those isn't really an opposition.
Yes, those support the war. Their claim is that they would be better at winning it then Putin.
There were few Russian individuals against the war, it does exist. But they are exception regardless of the camp they are in.