Hi

Yes after your B. Arch  from a recognised University in abroad you will be eligible for UPSC examination

This is because,

To be eligible for UPSC examination there's no need to be a graduate in a particular discipline,  all you need to be is a graduate in any discipline from a recognised university be it B. Arch, Btech, BSc or any other course.

You can check UPSC eligibility criteria below

*You must have a bachelor's degree in any discipline like  from a recognised university

*Minimum age limit :-  21 years

*Maximum age limit :-  32 years , also there's 3 year relaxation on upper age limit for obc and of 5 years for sc/st category

For detailed information go through

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

Thank you