There’s also a role called being an algorithms engineer in standard tech companies (typically for lower level work like networking, embedded systems, graphics, or embedded systems) but the lack of an engineering background may hamstring you there. Engineers working in crypto also use a fair bit of algorithms knowledge.

I do low level work at a top company, and you only use algorithms knowledge on the job a couple of times a year at best.

These days it's very different, mostly large-ish distributed systems.

I heard from someone who was in that field, that the main qualification for such a job is analytical ability and mathematics knowledge, apart from programming skills, of course.