Mask Aadhaar option allows you to mask your Aadhaar number in your downloaded e-Aadhaar. Masked Aadhaar number implies replacing of first 8 digits of Aadhaar number with some characters like “xxxx-xxxx” while only last 4 digits of the Aadhaar Number are visible.

You can download the Masked Aadhar Card by following the step-

Step 1: Visit official website of the UIDAI.
Step 2: Select 'My Aadhaar' from the drop-down menu.
Step 3: Select the 'Aadhaar Card Download' option.
Step 4: Enter your 12-digit Aadhaar number or other unique identifier (UID)
Step 5: Now, choose the 'Masked Aadhaar' option.
Step 6: Verify that the captcha code is correct.
Step 7: Select 'Send OTP' from the drop-down menu. (Alternatively, you can choose 'Enter TOTP.')
Step 8: Enter the OTP and download your Aadhaar or e-Aadhaar card, which is masked.

I hope this helps. Wish you a great eve!