Should an Engineering Manager make technical decisions?

It is not uncommon for EMs to be involved in technical decisions even in Big Tech. Many new EMs are pretty hands on and like to be close to technical details until they can't manage to be. However, just overriding a technical approach proposed by engineers is problematic. Finalizing a solution should be a team decision and the tech lead should be consulted with before deciding on a different approach. Totally agree with Alex about keeping the EM in loop from the beginning and seeking early feedback. It would help to have the solution approach in writing so that all the feedback is recorded and can be referred to later.

So there's 2 fairly separate problems/issues here:

1. Thrash
2. Engineering manager scope

Thrash

Thrash sucks, and I have seen the situation you mentioned time and time again (with the manager being a common culprit). The fix here is to communicate earlier and do more planning upfront. Before anyone in the team works on any major task, they should write down the approach in a doc/task and force the manager to read it (don't write any code until they give their blessing). These 2 resources should be helpful:

• System Design Masterclass: Taro Playlists - My doc in this playlist can be used as a template for technical direction discussion
• [Masterclass] How To Write Better Code Faster As A Software Engineer - This covers the planning approach alongside a bunch of generally good tips to ship code with higher velocity

Engineering Manager Scope

An ideal EM doesn't do any technical work, but that's more the case in larger, more mature companies. Since you work at a Series C startup, it is very, very normal for an EM to be technical as startups have more of a "Everyone does a bit of everything" vibe. When I worked at Course Hero, which is probably comparable to your company in terms of size, a lot of EMs would review a diff or join a system design discussion here and there.

If you want to learn more about EMs and their "ideal" styles, we gave a session on that: [Masterclass] What Software Engineers Should Look For In Their Engineering Manager

Isn't EM on the level of a technical lead but more towards people management, rather than sort of a Head of Engineering of the product?

This is generally what an engineering manager does, but it varies. As I mentioned before, the role of an EM is much more fluid at a startup, and this can also be the case in bigger companies as well (even FAANG) as Vaibhav mentioned. Back when I was at Meta, EMs would occasionally join system design meetings, review diffs, and even write some code. This is more common when a team is understaffed on engineers or the tech lead is lacking in some way (e.g. they are new or missing).

To make things even more complicated, Meta and Google both have an official TLM role (tech lead manager) where the person is both heavily technical and very involved on the people management side. There's a ton of nuance in how tech companies run themselves, haha.

All that being said, EMs being technical isn't inherently a problem. The problem here seems to be the thrash.

Isn't EM on the level of a technical lead but more towards people management, rather than sort of a Head of Engineering of the product?