[nbm]

Facebook (and probably many other companies) maintain an IC (individual contributor) track that doesn't entail becoming a manager or becoming some sort of architecture astronaut.

There are a few flavours of seniority for ICs - deep domain expertise, deep skill set, high productivity, high flexibility, able to design and communicate and drive large-scale changes, mentorship, and non-technical organisational leadership like running a training programme, improving hiring, and so forth.