There's bravery and then there's stupidity. I'm not sure what he thinks he can achieve as a prisoner in an Arctic prison (and presumably one day, a corpse) that he couldn't achieve as a free man, but I don't find his choice very aspirational.
True acts of bravery are done in the service of others, martyrdom is a pointless waste of human life.
What do you think Navalny would've been able to accomplish from afar? Him remaining in the West and subverting the Kremlin would have only fed the ideas that he's a Western agent.
He made a courageous and respectable move. The ball is now in the court of the Russian citizens on whether they want to fight for justice.
True acts of bravery are done in the service of others, martyrdom is a pointless waste of human life.