I'm in a similar situation, except making average salary only. Switched from academia to a software company recently. Right now I'm supposed to grok a 25+ years

I'm in a similar situation, except making average salary only. Switched from academia to a software company recently. Right now I'm supposed to grok a 25+ years old project consisting of about half a million source lines of well-hung legacy "C with classes" code. Of course it is mission critical code, of course there is no documentation. This is on the one hand challenging and overwhelming. On the other hand, there isn't much range for creativity, fun or purpose. One has to rescue that code and keep it alive and running for the next 10+ years. I know that once (if!) I grokked the stuff, I'm the only one at my company who can deal with it, meaning I'm stuck with it for an indefinite time. I try to stay positive and to be patient, because I heard that such situations are the normal. But my motivation suffers a lot. The good thing is, the people and labor conditions at the company are super nice. For me that is the main reason to stay, and probably I will stay at least until reaching "Senior Dev" status. But I can imagine to switch anytime, even back to research, and as soon there is some good opportunity (2 times the money would certainly do it). So I keep looking, applying, and try to persevere in the meantime.