If you think that the math part of game engines is interesting but aren't that interested in promoting an indie project, then you should look for jobs in robotics or computer vision applications. There isn't a large supply of jobs for replicating what can be handled by Unity or Unreal Engine.
What is it like to work in computer vision these days? I did some courses back in the day and it was interesting, but to me it seems that it's now devolved to looking up convolutional DNN architectures and trying which one works best for the problem at hand.
