Junior engineers should be able to drive smaller, well scoped projects.
Senior+ engineers should be expected to tackle complex, cross-org, ill-defined technical challenges, examples include technical mergers of company acquisitions, large scale migrations of business critical systems, technical design of big bets (also analysis on which big bets to take), evaluate new technologies/platforms, dev tooling to multiply productivity, etc
A lot of this requires buy-in and stakeholder management to succeed.