Discord does. It makes some sense, since Discord has a feature to broadcast what game you're currently playing (or anything you want), but I found it was scanning /proc even when I turned this off.

I didn't like that, and I spent a lot of time and effort working out various ways to keep it out of /proc (or anywhere else while I was at it- mostly with AppArmor) and ultimately ended up running it in a container with systemd-nspawn. This is still a little bit fiddly, but seems to work reliably and without any issues.

Wouldn't it be easier to just run it in a browser?

That's probably the better answer, yeah. I think there's a couple of features that don't work very well in the browser (push to talk?), but the actual answer is that it probably simply didn't occur to me at the time.

I use both these days.

The discord snap blocks this with apparmor by default unless you connect process-control. But it also fills your kernel log with audit denials.

I think I tried one of those alternative app distribute-y things at the time, but I don't remember which, and I came away disappointed. If memory serves, I couldn't establish whether it actually did any sandboxing, or what it did by default (like intentionally opening up this exact hole), and certainly not how to configure it, and gave up shortly in favor of something I'd at least seen before.

It might have been Snap. I don't like Snap.