Hello

Yes , after your mbbs you can give UPSC  examination.

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
And MBBS is a graduate degree , with mbbs degree so you fulfill the eligibility criteria of UPSC and thus you are eligible for it.

https://competition.careers360.com/articles/upsc-ias-eligibility-criteria/amp

Thank you