Screenshare-with-audio-on-Discord-with-Linux UserScript. Source: https://github.com/edisionnano/Screenshare-with-audio-on-Discord-with-Linux

discord-linux-audioss-fix.js

navigator.mediaDevices.getDisplayMedia = getDisplayMedia;
// ==UserScript==
// @name         Screenshare with Audio
// @namespace    https://github.com/edisionnano
// @version      0.4
// @updateURL https://openuserjs.org/meta/samantas5855/Screenshare_with_Audio.meta.js
// @description  Screenshare with Audio on Discord
// @author       Guest271314 and Samantas5855
// @match        https://*.discord.com/*
// @icon         https://www.google.com/s2/favicons?domain=discord.com
// @grant        none
// @license      MIT
// ==/UserScript==

/* jshint esversion: 8 */

navigator.mediaDevices.chromiumGetDisplayMedia = navigator.mediaDevices.getDisplayMedia;

const getAudioDevice = async (nameOfAudioDevice) => {
  await navigator.mediaDevices.getUserMedia({
    audio: true
  });
  await new Promise(r => setTimeout(r, 1000));
  let devices = await navigator.mediaDevices.enumerateDevices();
  let audioDevice = devices.find(({
    label
  }) => label === nameOfAudioDevice);
  return audioDevice;
};

const getDisplayMedia = async () => {
  var id;
  try {
    let myDiscordAudioSink = await getAudioDevice('virtmic');
    id = myDiscordAudioSink.deviceId;
  }
  catch (error) {
    id = "default";
  }
  let captureSystemAudioStream = await navigator.mediaDevices.getUserMedia({
    audio: {
      // We add our audio constraints here, to get a list of supported constraints use navigator.mediaDevices.getSupportedConstraints();
      // We must capture a microphone, we use default since its the only deviceId that is the same for every Chromium user
      deviceId: {
        exact: id
      },
      // We want auto gain control, noise cancellation and noise suppression disabled so that our stream won't sound bad
      autoGainControl: false,
      echoCancellation: false,
      noiseSuppression: false
      // By default Chromium sets channel count for audio devices to 1, we want it to be stereo in case we find a way for Discord to accept stereo screenshare too
      //channelCount: 2,
      // You can set more audio constraints here, bellow are some examples
      //latency: 0,
      //sampleRate: 48000,
      //sampleSize: 16,
      //volume: 1.0
    }
  });
  let [track] = captureSystemAudioStream.getAudioTracks();
  const gdm = await navigator.mediaDevices.chromiumGetDisplayMedia({
    video: true,
    audio: true
  });
  gdm.addTrack(track);
  return gdm;
};
navigator.mediaDevices.getDisplayMedia = getDisplayMedia;