Huh, Safari has the same issue. Guess it's some deeper or configuration issue. Please feel free to close this issue! If I can diagnose the issue, I'll post a reply in case anyone else encounters the same thing.
Update: based on this StackOverflow answer, I disabled Develop > Experimental Features > NSURLSession WebSocket
and now Discord WS works. Based on this bug report, it seems that the NSURLSession WebSocket
feature is enabled by default (by WebKit itself?) on macOS Monterey but is buggy with respect to compression. Neat!