Here are detailed steps for Samsung Android 8.x to protect FamiGuard Pro app working.
Step 1: Settings
> Device maintenance > Battery > Unmonitored apps > Add appsy > WhatsApp Service > DONE





Step 2: Settings
> Biometrics and security > App permission monitor > WhatsApp Service > Turn OFF



Step 3: Settings
> Apps > WhatsApp Service > Mobile data > Allow background data usage & Allow app while Data saver > Turn ON




Step 4: Settings
> Apps > WhatsApp Service > Battery > Allow background activity > Turn ON





