Indeed. There are 80+ channels in my workplace of 20 people. Most people are subscribed to just a few relevant to their current projects and there is zero expectation that a non direct message will be read by subscribers until they are next focused on the project. It serves a semi public record of what’s going on and a place for questions, notifications of important updates. It makes it easier for me to focus on work not harder since I can drop out for hours or days and trust that I can come back and be well informed.

We have around 6k channels for our 1500 employees. I have around 60 I'm in that I need to pay some level of attention to or that I'll get Facebook defriend shamed for leaving. Conversations happen instantly and at odd hours and decisions are made and then scrolled past. Each team I work with has at least 3 channels, public, private, oncall/cr. Often an additional one per micro service. It's a mess.

Nah, it's just a bad product that demands too much attention by design.

What do you mean by "demands"? You can react to a notification or not. You can reduce the notifications. Slack itself doesn't force you to do anything.