To add or sync your iCloud in Mail for Windows, follow these steps mentioned below.
There is just one thing to set up your iCloud in Mail for Windows, you will need to generate an app-specific password to add your iCloud account to the Mail app, that is, if you have already enabled two-factor authentication on your iCloud account,
1. Go to your Apple ID and sign in to your Apple ID account page.
2. Under App-Specific Passwords, select the Generate Password .
3. And now follow the onscreen instructions to finish the setup.