@gabrielayuso.eth
This is a good list in terms of the tech and concepts specific to backend. I don't necessarily agree on going too deep on a stack but I'm biased since I've always been very stack agnostic. There is value on both depth and breadth.
However, a lot of this can be known and done by a Sr SWE.
At Staff level you are more equipped with dealing with ambiguity, evaluating trade-offs, prioritizing, designing systems with larger scope and/or impact, working with many stakeholders (customers/users, upstream/downstream dependencies, large cross-functional teams), etc.
In the age of AI these skills are significantly more important than knowing stacks deeply. You're still the ultimate decision maker though so be good as evaluating trade-offs and making decisions that are more future proof and that scale.
https://x.com/i/status/2013908799015498169