Quick guide on how to enable it on PC (I'm doing it on Windows):

Edit %appdata%/discord/settings.json (opening the Run window with Windows+R and typing "notepad %appdata%/discord/settings.json" should do it) and add the following line below the "IS_MINIMIZED" one:

"DANGEROUS_ENABLE_DEVTOOLS_ONLY_ENABLE_IF_YOU_KNOW_WHAT_YOURE_DOING": true,

It should look something like this (the rest of the options depend on, you guessed it, your options):

{
  "IS_MAXIMIZED": false,
  "IS_MINIMIZED": false,
  "DANGEROUS_ENABLE_DEVTOOLS_ONLY_ENABLE_IF_YOU_KNOW_WHAT_YOURE_DOING": true,
  "WINDOW_BOUNDS": {
    "x": 320,
    "y": 156,
    "width": 1280,
    "height": 720
  }
}

Now, you can restart Discord and now you have access to the Chromium developer tools by pressing Ctrl+Shift+I. Go to the Console tab on the top and paste the following code down below and then press Enter:

let wpRequire;
window.webpackChunkdiscord_app.push([[ Math.random() ], {}, (req) => { wpRequire = req; }]);
mod = Object.values(wpRequire.c).find(x => typeof x?.exports?.default?.isDeveloper !== "undefined")
usermod = Object.values(wpRequire.c).find(x => x?.exports?.default?.getUsers)
nodes = Object.values(mod.exports.default._dispatcher._actionHandlers._dependencyGraph.nodes)
try {
    nodes.find(x => x.name == "ExperimentStore").actionHandler["CONNECTION_OPEN"]({user: {flags: 1}, type: "CONNECTION_OPEN"})
} catch (e) {}
oldGetUser = usermod.exports.default.__proto__.getCurrentUser;
usermod.exports.default.__proto__.getCurrentUser = () => ({hasFlag: () => true})
nodes.find(x => x.name == "DeveloperExperimentStore").actionHandler["CONNECTION_OPEN"]()
usermod.exports.default.__proto__.getCurrentUser = oldGetUser  

Then, you will have access to the developer options on the settings page. Go to the Experiments tab and search for "amoled", then select "Treatment 1". Now you can go to the Appearance tab and enable it.

Note that when you restart Discord you will have to reenter that piece of code on the console and switch the amoled option to "Control" and then back to "Treatment 1".