There are some great suggestions already, however, it sounds like many comments are focusing on their experiences as a tech manager and not the interview preparation, which was your question.
I interview a lot of technical managers, and beyond technical chops, I focus mostly on communication skills, charisma, and personality.
I tend to ask a lot of behavioral/situational questions to understand how the candidate would handle different situations and how his personality lines up with the team. We are usually hoping for a thoughtful and genuine answer.
Additionally, I often schedule lunch with the candidate and the key players on the team, without the participation of the recruiting team, so they can speak freely.
You can prepare for some of the situational questions but keep in mind that it is totally ok to say "I don't know" or "I have not thought of that".
I interview a lot of technical managers, and beyond technical chops, I focus mostly on communication skills, charisma, and personality.
I tend to ask a lot of behavioral/situational questions to understand how the candidate would handle different situations and how his personality lines up with the team. We are usually hoping for a thoughtful and genuine answer.
Additionally, I often schedule lunch with the candidate and the key players on the team, without the participation of the recruiting team, so they can speak freely.
You can prepare for some of the situational questions but keep in mind that it is totally ok to say "I don't know" or "I have not thought of that".
Best of luck!