Also, the sibling commenter mentions one of the big reasons I found so much joy in it. This kind of hardcore technical support is in many respects closely related to working on greenfield projects. In my experience, the fun stuff usually ends up with some unfun caveats like company bureaucracy, office politics, or having the tech stack chosen beforehand, this kind of thing. But there's an interesting inversion when a company's production environment is broken and you're the one that can fix it. Obstacles magically disappear and you have a tremendous amount of freedom to do your job, with effectively two different companies doing what they can to enable your work, because the only thing everyone cares about is getting it working again.
You do have to be able to walk the walk -- and I cannot stress enough that it takes a certain type, and just knowing your shit isn't going to cut it -- and you also have to get some personal enjoyment out of chaotic environments, and be able to talk people out of a tree sometimes. But you'll never run out of new and interesting problems to solve, you'll be testing your mettle far more frequently than your peers, and you'll be expanding your professional network every week about as much as everybody else does once or twice a year when they go to a convention. It's the closest thing the tech industry has to a firefighter or superhero or something.
Recently a client asked if I can help reverse their own android app because the developers were holding their source code hostage. It was lots of fun and lots of struggle but overall satisfying.
Maybe something like basic security freelance work especially basic webapp security(xss,sqli,csrf, the likes) and some process security with maintaining proper logins, maintaining and rotating credentials etc.
Thank you for your ideas.