Don't be a socially distant manager
Especially when you are first promoted into management, having some social distance between you and your direct reports is a good thing. No longer are you just one of group, you are now the boss. Behavior that would be fine before, will no longer be acceptable and could actually alienate and demotivate folks on the team. Managers who navigate this well have success in their first manager gig, but a lot of manager's need to wait for their second gig (when they inherit or build a team, rather than get promoted into leadership from within the team) to truly thrive.
So, some decorum as a manager is good. However, being truly distant - or going the entire other way where you fail or refuse to build connection with folks that you manage - is in my opinion sub-optimal.
I struggle with calling this short coming "bad". Ultimately, I don't think being in connection with the folks on your team is an enumerated part of the manager's job description. There are probably effective managers out there who are quite distant and they, by all accounts are successful, but I want to posit that this is not optimal. A manager who can maintain professional decorum while engaging with the people they manage as people will ultimately drive better outcomes and be a more complete leader.
So what is this personal / professional relationships-line between managers and the people they manage? Ultimately, it comes down to understanding the needs, motivations and circumstances of the people you are working with. A great manager is curious about the people they are working with. Why are they here? What is going on in their life that is impacting their personal and professional decisions? Why do they come in late in the mornings but stay late in the evenings? Who are they and what do they want?
A manager who is disinterested in the personal factors of the people they manage will miss a lot of opportunities to improve team dynamics, retain top performers and ultimately, they will be the one who suffers most as they leave their position without having developed new relationships. Work is a long and winding road and interpersonal connection with the people you manage can create relationships that go beyond just that one stop on your career journey.
How do you cultivate this? To build connection as a manager, means going first. You need to open up about your needs, motivations and circumstances with the people you manage. This needs to be authentic. If its on your mind, and appropriate (at the start or end of a meeting) and the topic is at a level you would feel comfortable sharing with an adjunct in-law or friend from high school, you can share it with that person you are having a 1:1 with. This sharing will open the door for them to possibly share with you in some future encounter. Over many such meetings, your understanding of them (and they of you) will grow and pay dividends.
I don't want to come off here as too formulaic. The ultimate goal for you needs to be your own fulfillment in having a full and rich life of which work is a component, but taking this first step of sharing first can set you on the path to becoming a more complete manager and better leader as well as a happier more fulfilled person.