How do people make friends?

26M moved to a new city 3 years ago for graduate studies. In last 3 years I have only met 5 people (3 of them were my ex-roommates) and 2 of them are my current roommates). And can only call 1 of them a friend and he moved out a year and half ago too.

Had a few friends from undergrad but we parted ways. They are working and have made new friends and I haven't met them since graduation, we do call each other once a year.

I am an introvert and socially awkward, don't know how I made friends in undergrad at the first place.

I try to go to college events and talk to people but it usually ends up being a discussion on each other's research and I don't know what else to talk about.

My mom was always concerned about my social life and now I feel like she was right all along.