I just did a fresh Arch install with Sway + Wayland and refrained from installing XWayland. Slack opens perfectly fine with the ozone flags and everything appears to be working but when I tried to upload a file, it opens the file dialog and when I hit Open nothing happens.

Retried with WAYLAND_DEBUG=1 but could not spot anything. It's very verbose, I grepped for file and the filename but nothing interesting came up. Also considering this may be Arch related, a specific package that I might be missing? This should work assuming this is just the File API that Electron is utilizing.