When COVID forced us to work from home, I initially resisted installing Slack on my computer. I don't like Electron, and I'd set up my machine such that installing Electron apps was technically difficult anyway.
IMO, the UX was horrible. I tried to keep Slack as a pinned Firefox tab, but it was far too easy to accidentally move over to a different website, at which point I stopped getting notifications. I also felt like I had to constantly keep my web browser open—I can't say why that's substantially different than having to keep a Slack application open, but for some reason, the separate dock icon helps me to mentally compartmentalize.
When I finally switched to a standalone Slack app, it felt much nicer.