[nish93]

It is not mandatory for NRIs, only indian residents. Refer below:

Aadhaar-PAN linkage requirement does not apply to any individual who is:

Residing in the States of Assam, Jammu and Kashmir, and Meghalaya; a non-resident as per the Income-tax Act, 1961; of the age of eighty years or more at any time during the previous year; or not a citizen of India.

https://www.incometax.gov.in/iec/foportal/help/e-filing-link...