working for a narcissist - stay and play the game or leave?

Need some real advice from people who’ve dealt with this. I’m a mid-level manager, doing well at work, leading projects with C-suite visibility, handling 60% of the team’s workload, and have strong relationships with senior leadership including the CEO, COO, CCO, so on paper it’s a solid role. A large govt company with stable pay etc.

But my department head is a complete narcissist. She’s hot and cold, supportive in private then undermines me elsewhere, steals credit and downplays my work, has blocked my promotion with no clear reason, and recently hired someone above me who’s not technically competent with less relevant experience above me and moved my reporting line to him which basically caps me. She’s also tried to reduces my visibility, and the criticism only increased once I started getting recognition. It’s starting to feel intentional rather than random.

I’ve built real credibility at my job, the kind that takes years to build, so leaving means walking away from that. I’m interviewing and hoping to get better offers in terms of pay and title. So I’m stuck between staying and managing her while playing the long game, or leaving and starting fresh somewhere healthier.

For those who’ve dealt with narcissistic bosses, does this ever improve or does it just get worse? What would you do? How do you sane through this?