Well, basically you then need to chase them as a dev manager. And not just one person, but most of the team, because you can't really get the information passively. I bet the devs love that. In practice this doesn't really happen and the dev manager is quite blind to what's happening.
And it's not just the dev manager, but generally all team members get this information passively when co-located. It's much easier to read the room when people are in the same place, and you see how they interact. When remote, devs often have no idea about other devs, unless they again chase the information (which usually doesn't happen).
> Well, basically you then need to chase them as a dev manager
What you are describing, following them around to observe what they are doing, sounds a lot more like "chasing them" than asking a couple of follow-up questions in the standup.
And it's not just the dev manager, but generally all team members get this information passively when co-located. It's much easier to read the room when people are in the same place, and you see how they interact. When remote, devs often have no idea about other devs, unless they again chase the information (which usually doesn't happen).