Instead of typing, you can send a quick voice message by tapping the microphone icon in the chat composer. This starts recording immediately, with a live timer showing how long you've been recording.
While recording, you can either cancel it (discarding the recording entirely) or tap send to finish and deliver it to the conversation. There's no need to hold the button down the whole time — tap once to start, then tap again to stop and send, or cancel if you change your mind. Once sent, the recipient can play it back directly in the chat.