Compose and Mod3 keys do not work

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Steps to reproduce

1. Type a message, attempting to use the Compose key.
2. Again, this time using Mod3 (usually AltGr).

Expected behaviour

I should be able to type accented characters etc. using these methods.

Actual behaviour

I can't type accented characters using these methods. There's nothing to show!

Diagnosis and logs

{
  "launchAtStartup": false,
  "theme": "default",
  "systemTitleBar": true,
  "monochromeTrayIcon": false,
  "zoomFactor": 1,
  "playSoundChat": "respect-dnd",
  "playSoundCall": "respect-dnd",
  "enableCallbox": "respect-dnd",
  "secondarySpeaker": false,
  "secondarySpeakerDevice": null,
  "trustedFingerprints": []
}

Insert error logs here.

I have no problem using Compose and AltGr in the web version of Talk.

Start by reproducing the Compose and Mod3/AltGr behavior in the Linux desktop client and compare it with Talk in the web version. Review the client logs and the desktop input-handling entry points to determine where these key events are lost. Done means accented characters can be entered through both methods without breaking other keyboard input.