An audio clip with a play button, sent like a file. It plays in one tap on phones and computers. It isn't the chat app's own voice-note bubble with a waveform: WhatsApp, Discord and the others draw that only for recordings made inside the app, and no outside tool can send one from a computer.
Every clip carries an inaudible watermark and a label saying it was made by AI, and anyone can check a clip. Use your own voice, or someone else's only with their permission, and tell people it's a typed voice note when it matters.