Hi da652,
Thank you for participating in the Apple Support Communities. We understand that you'd like to set up Focus to allow notifications for WhatsApp for specific people, and we'd like to assist. We've noticed you've come from a helpful article for Focus:
Use Focus on your iPhone, iPad, or iPod touch
It sounds as though Focus may not be working properly if you've added both people and the app. Have you restarted your device since this issue began? Do you have the latest version of iOS and WhatsApp?
Update your iPhone, iPad, or iPod touch
We look forward to learning more about your issue.
Take care.