I wonder how much of that comes down to culture. Since going remote I have come to wonder if a direct-message-first chat culture is harmful to collaboration.

IMHO most companies encourage public-first conversation, but still end up with DM-first as their employees don't have enough trust in how their messages will be received.

It requires to be comfortable exposing lack of knowledge or saying weird things to peers, and be confident it will be taken in good faith. As you point out, that requires a whole level of culture building.

DM-first is an extremely frustrating culture. That kind of operation tells me that that folks are too risk averse and political to discuss things openly. Typically this is led by panicky managers that are worried about involving too many people or having to explain things to folks they don’t want to deal with, and it escalates from there and gums up ALL the things. It makes Slack basically useless.

The same people DMing however will also extol the virtues of posting in public and lament why there is not more conversation happening in the open.

It is. You need to be aware of it and have people that can set examples about chatting in public rooms or who can recognize when to stop a dm chat and move to be public

I hate direct messages. They were normally considered rude in IRC.