Basically, an L5 (or equivalent level at other companies) is supposed to be largely independently competent (but not necessarily excel) in most engineering areas. They understand the context enough to determine which projects are important (including those they might make), they can identify stakeholders and communicate status and needs well enough, they can project manage enough (or make a project manager successful), they can work through others to a reasonable degree, and so forth. They'll know those areas they'll never be good at, and have some mitigations in place for those. They're self-motivated, think about their work holistically, and generally will navigate the delivery of the project without guidance - but when they need it, they'll make sure they get it.

From an interview point of view, they're probably looking for examples of that independence and self-motivation (ie, not just doing what someone told you to do), and also the step beyond just writing the code towards more holistic ownership (things like "created a new test harness along the way", "did a survey of developers", "made sure there was a killswitch", "created a rollout strategy", "convinced another engineer to share review and support responsibilities").