First, I would keep the "Do Not Track" option but add a clear notice explaining its limitations and the fact that many websites do not respect the special HTTP header signal. Instead of removing it completely that allows for a chance of them respecting the special HTTP header signal, users who still want to use it can do so and with a full understanding of its lack of guarantee in its effectiveness.
Simultaneously, I would focus on educating users about the new, more robust privacy features like Enhanced Tracking Protection and Total Cookie Protection. Over time, as users become more familiar with these stronger privacy measures, I could gradually phase out the "Do Not Track" option, ensuring a smooth transition without leaving users feeling like they've lost a privacy tool.
This approach balances maintaining user choice while steering them towards more effective privacy protections.