hey there
BA LLB will be definitely helpful for you if you want to do UPSC but its not like without it you cant clear the exam. In BA LLB you will learn a lot about constitution of india its different sections and about IPC which is in UPSC. Rest you have to prepare like history, CSAT etc.
check the link
https://competition.careers360.com/articles/how-prepare-for-upsc-ias
good luck
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