To minimize Meta AI's presence on your phone applications like Facebook, Instagram, and WhatsApp, you can mute its notifications or chats, as complete removal isn't currently possible.
Facebook & Instagram:
Open the app and tap the message icon.
Select the Meta AI chat (identified by a gradient circle).
Tap the "i" icon in the top-right corner.
Choose "Mute" and select "Until I change it" to stop notifications