I look at it as follows:
Developers have the following core competencies: project management, ui/ux, distributed architecture, programming (including programming tests and devops), security, and data management (sql, back-ups, etc). Obviously people are going to specialize at some point, and some systems need entirely different skills, and I'm leaving out SAs, DBAs, UX designers, Product owners, but for most work you need a team that can cover all that, and imo, senior developers should have a pretty good handle on all of that even if they specialize in one area. (By project management, i don't expect them to be project managers, but they should know how projects go down from start to finish)
As an engineering manager your core competencies are vision (do you know what needs to be done), leadership (can you sell a vision and get buy-in), administration (follow sdlc, do all the HR stuff), and mentor both junior and senior people in all of their core competencies.
Your main job is to deliver in the short term but also build a more capable team. If your senior staff know more than you, that's awesome, as long as you can tell when they are getting off-track.
It's a big space to operate in. Few do it well and most dev managers get by ok for decades basically sucking by this criteria, so don't be scared to just jump in.
Most days, I'm not sure I do it well, but that is the framework I use to guide myself and evaluate other managers. The vision/mentoring comes pretty easily to me (i have a very strong dev and architecture background), the leadership, especially up and across the org chart? Well, let's just say I'm working on it.