What you’re describing are just run of the mill backend jobs. They aren’t very sophisticated in terms of algorithms or theory. What I had in mind is working on say Cassandra or ElasticSearch, or internally within FAANG on one of their database engines. If you’re high enough there (which, granted, may take multiple years) to decide on the future direction of the engine, you get to ponder a lot of theoretical or at least very complex stuff.
I did try applying to MongoDB a few times, even made it relatively far in the interview process both times but eventually get the "We regret to inform you..." emails for it. I also failed a phone-screen for CockroachDB though I'm actually not 100% sure why. ElasticSearch never got back to me. I certainly applied for these kinds of jobs (and many, many more), but there's not much more I can do than wait for the companies to recognize my brilliance.
When I worked at Apple I did an internal interview for a team that worked on a distributed-RAID-style thing, did really well on the interview, almost got to the offer stage, but then they saw the previous year's review where I got a "Needs Improvement" for (I think) purely bureaucratic reasons that I've talked about on HN before, and they decided not to move forward.
It's tough, because I think a lot of those jobs are in pretty high demand, and as such a lot of really qualified people apply to them and they can be picky, and I don't really blame them for that. There's a lot more generic unsexy backend jobs.
