If this is something you're looking for, my recommendation is to look at either large companies that have large infrastructure needs (Google, Facebook, Twitter, Amazon, LinkedIn, etc.) or small infrastructure-related startups, depending on your preferred working environment. If the hard parts of your job are offloaded to the database/language runtime/middleware, look for companies that work on databases, language runtimes or middleware. And in the interview, ask them for examples of hard problems that they have solved.
Also, I have absolutely nothing against the companies that don't do this kind of work. In fact, Firebase exists so others don't have to do this kind of work. This is just an observation that occasionally, the skillset tested in these interviews is not in line with the responsibilities a successful candidate will end up having, so make sure you ask.