One thing that’s problematic is that Slack has the “wrong” notification settings on by default (it notifies you of everything). You should flip the default to “mentions only” and then don’t worry about looking at a channel unless you’re mentioned. Once you’ve got that setup the channels start working to your advantage because you can use them as topic headings to just read the stuff you’re interested in keeping up with once or twice per day. Then you can press shift+esc and clear all of your unreads (or do the same in the “All Unreads” section IIRC).

As for the emoji: If you ever aren’t sure what one means, just hover over it (on desktop) or press and hold on a reaction emoji on your phone and either way will show you the its name which usually gives you a pretty good idea of its meaning.