I don't really have to work that many hours in my SWE job to be productive enough to satisfy management. I could easily take on a second job if it was like the

I don't really have to work that many hours in my SWE job to be productive enough to satisfy management. I could easily take on a second job if it was like the first. And I would happily do this to double my TC. I'm honestly sitting around bored a lot of the time, waiting for code reviews or running long pipelines or builds. Assuming this is legal, how exactly would it be so unethical to do this? If I could work a second job without detriment to my performance in the first, what's the harm? Also, is it legal?