Tried that, they actively employ darkpatterns to coerce users onto desktop apps. I even asked them to stop asking for an app install on their links that you open from inside the webapp and they told me to get stuffed and use the desktop app.
Yea, I use Matrix integration when I deal with Slack, that way I have my choice of client and there isn't any code of Slack's running on my machine.
Strange, after declining message about "native" desktop app, I've never seen it again. No other issues as well. Firefox 69 on Windows, one paid and one free workspace.