[OthmaneHamzaoui]

As mentioned by gregjor business pay people to solve business problems but given your interest in pure tech I would look for companies who's core business is something purely technical (example: DevTool companies are a great place to start).

Unsure what you mean by "senior" roles, but in most large companies it's what you described as not wanting to do: tech + non tech responsibilities. If by seniority you mean owning a larger piece of the codebase and solving challenging problems I would look more for roles of "founding engineers" or simply "software engineer" at early stage startups (again building software that has a technical edge).

The smaller the organisation and the more its business is purely a tech product in itself the more likely it will align with what you're looking for (+ you'll be surrounded with like minded engineers). Hope it helps :)