Russians supported the war when it was a largely professional army doing the invading. Support for war is typically thought to decline when your own family members get dragged into it and injured. Drafts have never been popular politically.

i think we can conclude with high confidence that those paying ~1000€ for a plane ticket to flee before mobilization, aren't actually supporting it

I think the only thing we can conclude from that is that they're not willing to risk their own lives for it. It says nothing about their overall sentiment about the invasion itself.

By what independent survey? citation please