You must understand: remaining quiet is the way of life in Russia. You learn from a young age: shut up and go about your life, or be bullied and ostracized. Don't rock the boat, and you may retain the prospects of a good life in the country. Russian people have been bullied for centuries in this fashion.
Outside of that, people higher on the social ladder in Russia, like Pugacheva, have to work with Putin's government (or at least stay quiet about it) to not lose their status and prospects of earning the good money. If you're an artist who's an enemy of Putin's, you can't work in the country as long as his cronies rule. (It doesn't hurt that Alla may or may not have the right of long-term residence in Israel. This comes with being the wife of a Russian artist of Jewish descent Maxim Galkin, who'd been openly critical of Putin's government in the past and has been recently listed as a "foreign agent": an official brand of Putin's disgrace.)
In other words, unlike in the US, in Russia it's rare for a person of such stature to stand so openly against the bullshit the government's doing. You must remember: while US' democracy is flawed, it's still a democracy; Russia is a dictatorship, more so since the war's start.
While it doesn't cost her very much to speak up (she can still perform around the world, and Israel is a haven for the former-USSR/Russia citizens, many of whom grew up listening to her songs), what makes this different is that, like the article says, Pugacheva is extremely popular in Russia.
More than anything, it shows that Putin's losing the respect of more and more people high on the social ladder. Many a star of the Russian media either align openly with Putin or stay quiet, but the more the popular people – those having the attention of the public – speak up against him, the less control Putin et al. retain on the country's politics.
Plenty of commentators in my Ukraine feed treat it as a tidal shift in public opinion in the country. I reserve joy until I see Putin toppled, but this is great to see. Maybe it will sway some opinions. The zeitgeist is stirred by opinions spoken aloud, after all.