need to generate in app password but it does not give me an option under security as instructed

You need to enable 2 Factor Authentication on your Apple ID to be able to create an app specific password to use. If your account won’t allow 2 Factor Authentication, try 2 step verification.

Apple ID -Two-factor authentication

Two Factor Authentification availability

Apple ID - Using app-specific passwords

Apple ID - Two Step Verification App Specific Passwords

Apple ID - Two Step Verifications FAQ

You need to sign into your Apple ID account page: Apple - My Apple ID to create an App-specific password. It is not related to iCloud.

Cheers,

GB