Hi

You can choose any subject  of your choice based on your interest after your 10+2 for your graduation,

this is because to be eligible for UPSC or the IAS 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 as your stream can be really helpful for your UPSC or the IAS 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.

Thank you