Hello Abhishek!
Not only NIFTians (holding a B. Des. or M. Des. degree), but anyone, irrespective of the course and degree one holds, is eligible to appear in UPSC or any Government Examination. The only eligibility critera is that you ought to be a graduate at least or in the final year of graduation in any field/subject. Eventually what matters in UPSC or in any other government exam is your in-depth grasp of the subject that you choose to study for the exam, your language skills, general knowledge and current affairs.
All the best! Do well! :)

Hey Abhishek!
Hope you are doing Well :)

Yes, dear It doesn't matters even if you are a NIFTian,you can Definitely Apply for UPSC  or any other Government exams once your graduation is over.

Hope so my answer works!
If not do tell me :)
All the best dear !
Keep Smiling :)