I work on performance and I enjoy it even more than writing features, honestly. There’s much more freedom in it in a professional setting because you generally get to define the subtasks under the goal of “make it faster/more efficient” whereas with a feature you’re usually told what specific thing you’re supposed to make, and your flexibility is usually just picking how to implement that. And the problems are almost always challenging and require technical (and occasionally, political) insight to fix. With features you might ship something that’s loved or a dud, but improving the performance of something is basically always a good thing.
I'm currently at a very big company (not faang) and I had the chance to do a little bit of performance analysis.
But unfortunate it was a totally unoptimized thing so only quick low hanging fruits.
Like io bound but they didn't though that component is the issue as it was not CPU bound, bad SQL queries and unoptimized caches.
Nothing big or difficult to analyse :-(
I learned about one person who is only doing java Performance analysis and he said it took a while to be known in the industry good enough that he can do it fulltime.
And he has to travel to allot of customers.
The principle to do whatever you love is to "ask for forgivness not permission". Feel free to understand why you're solving what you're solving in order to challenge it and do it right.