I am an Android developer with 3yoe. i want to make a transition to full-stack or backend. Is it possible?

It's definitely possible, but depends on your work environment and support if you want to do it in your job. Following courses and creating projects will help you in that. I've known people who did that.

What’s wrong with android? I’m a full stack developer and I think android is freaking cool. I’m also jealous that I don’t get to work on the cooler stuff like advanced infotainment systems, self driving stuff, VR etc. Your typical React SSR with Java backend is boring but distributed computing is the coolest!