Turn off Read Receipts in WhatsApp settings
Go to WhatsApp Settings
Tap Privacy
Disable Read Receipts
Use Airplane Mode before opening the message
Open WhatsApp while offline
Read the message
Close WhatsApp completely
Turn off Airplane Mode
Disable internet access before reading messages
Read messages from notification preview
Use WhatsApp widget to preview messages
Restrict WhatsApp background data
Use a third-party app only if you trust it and understand the risks