For that I use the Discord API for python which is normally used to control a bot but which I used to control my Discord account.Thanks to that I could send message on discord with an simple python script. For that you must run the bot with your discord account's token and add Bot=False when you launch the client with yourBot.run("your Tokken", bot = False. To get you discord account's token you just need to find it in the navigator windows on any search browser.
Then I use 3 ios apps to add it to Siri:
- Shortcuts
- LibTerm
- Scriptable
LibTerm is a free app that provides access to a command terminal. With that you can execute any python script on your phone and install and import libraries like Discord.py. Also it give you a block in Shorcuts to run any command.