Hi

You can choose any subject  of your choice based on your interest for your graduation after your 12th

This is because,

to be eligible for UPSC or civil services  examination there is no compulsion to be a graduate in a particular subject, all you need to be eligible is that you should be a graduate in any discipline

So you can choose any stream of your interest, but yes if you are interested in Arts then

choosing Arts or the humanities can be really helpful for your UPSC  examination, this is because in Arts you will be learning subjects like history , polity etc which are a part of the UPSC syllabus so it will help you in your upsc examination.

Thankyou