My essay focused on Ubuntu on ARM and how critical it would be for hyperscalers, which at the time wasn't really a thing at all (that should date me).
I ended up declining their offer mostly because nowhere during any step of the process but the very end they pointed out they could only contract, not take me on as a full-time employee.
I don't regret giving it a go, but it was one of the weirdest hiring processes I've ever gone through (including FAANG, MBB and think tanks).