Why can’t I add cards to wallet and also Apple Pay cannot be setup on my iPhone 11 Pro in India

See -> About billing for Apple subscriptions and media products in India

About billing for Apple subscriptions and media products in India - Apple Support

India

•           Apple ID balance (from adding funds)

•           Net Banking (adding funds only)

•           UPI (adding funds only)

You can use / pay with your Apple ID balance, see: Add money to your Apple ID balance

Add money to your Apple ID balance - Apple Support (IN)

As you can see here, Apple Pay is not supported in India.

Countries and regions that support Apple Pay - Apple Support