Managers should never write or review code. This is a fundamental principle of human work, it has nothing to do with code itself. Honestly I don't know what insane HN meme started this trend and made it acceptable, but it really needs to end now.
The whole point of different roles doing different things is distribution of labor [1]. This idea is thousands of years old, this shouldn't come as a shock. As an extreme oversimplification, the people who are very good at a particular thing, should focus on that one thing. The more responsibilities or tasks someone has, the worse their output will be. Specialization enables higher quality, faster work, with less difficulty and waste.
A coder's job is to write code. A manager's job is to manage people. The author's post listed nine different important responsibilities for managers, that has nothing to do with code. But then just brushed it off, like it's easy! People, these aren't easy things to do, nor are they quick! Just doing general management work will easily suck up 40 hours a week on any team. If you've run out of management tasks, you probably aren't managing well.
Almost every manager I have had has not performed well. With the exception of one, they never trained as a manager, nor read or understood the basic yet critical functions and skills of a manager. Some of them used to be engineers and were just promoted up to a job they are incompetent at (the Peter Principle). And some moved into the position from some other job that wasn't management (or engineering management). On top of that, often there is a shortage of project managers, product owners, etc. These are critical roles to ensure high-quality, faster output for a team. In the absence of people filling those roles, and on teams that are not high-performing teams, it's up to the manager to fill those roles for their team.
So now the manager is not only responsible for the careers of their direct reports, they're responsible for keeping the team on track and producing high-quality, fast work. I've only ever seen one or two managers that could accomplish this feat - and that's before we add-on writing and reviewing code. How the hell are they supposed to get the time for all this, much less build up expertise in all these things, simultaneously?
I would argue that knowing how to code at all makes for a dangerous manager. I've had several managers turn into micro-managing freaks, telling me how to do my job, even preventing me from doing my job. They insisted they knew better, because they had written some code in the past, or adminned a server one time... yet I'm the one with the most experience and skills in that field. (Dunning-Kruger seems worse in those with authority, who don't wield it with humility)
On the other hand, the most effective manager I have ever had, had zero idea how to code. Because he was not technical, he focused on his actual job: mobilizing groups of people towards a task, measuring its progress, helping resolve human challenges, protecting his direct reports, and helping them progress in their careers. He never once told me how to do my job. He instead asked myself and my peers a series of simple questions in order to have us explain what we were doing, and through that process, we actually discovered several times that we should do it differently, or solved our problem.
So if the manager isn't writing or reviewing code - who will?!
An engineer's job is to build things. So someone who specializes solely in engineering should be reviewing code, designs, etc. There are many different roles for people who do this - software architect, systems architect, engineering team lead, staff engineer, principal engineer, etc.
A long, long time ago, the whole point of having "Senior" in your title was to convey the fact that you were an expert in your field. If there was a "Senior" engineer, that was the person you went to to tell you if you're doing it right. Hey, I just wrote this algorithm, does this look okay, Senior Engineer? I'm changing this field, can you see anything that might go wrong, Senior Engineer? Now of course it just means a college grad got a promotion after staying for 2 years.
Not having a real Senior Engineer somewhere in the company means you are going to end up making some real turds. Having a manager take the place of a Senior Engineer doesn't help, because they can't do two completely different jobs well. You can't be both a great plumber and a great electrician. You can half-ass both, though, and get half-assed results.
If you're a manager and you want to have a high-performing team, stop writing/reviewing code, and instead do everything you can to implement the suggestions here [2]. There is an enormous amount of work needed to achieve these suggestions, so you will not have any time to look at code, I guarantee you. But your team will end up working much better, producing better outcomes.
[1] https://en.wikipedia.org/wiki/Division_of_labour [2] https://dora.dev/research/?view=detail