Can i create an app that does something when im in a specific chat in Whatsapp?

I want to make an app that locks specific chats in Whatsapp with a passcode/fingerprint.
Thank you.

Thats not possible and whatsapp would never allow something like this you cant take control over whatsapp like this. Simple answer its not possible.

I saw simillar apps that do that, and I don't want to publish this app

Actually in WhatsApp? The WhatsApp API looks rudimentary:

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