To stop enter key from sending messages in ChatGPT, you need to hold down the Shift key while pressing Enter. When you press the Shift and Enter keys together, it will move to the next line, allowing you to write your message on the next line without sending it.
How to go to next line in ChatGPT?
To move to a new line in ChatGPT while typing a message, on desktop devices and browsers, you should press Shift-Enter together. When you press Shift and Enter keys, you can continue writing on the next line.
This combination will also stop enter key from sending the message.

In ChatGPT’s mobile app, to move to the next line, you need to press the Return key located in the bottom right corner of the keyboard.

What to do if pressing enter no longer submits?
Some users may experience an issue where ChatGPT no longer sends messages when they press the Enter key. This problem is often related to temporary disruptions in the JavaScript code for various reasons.
To resolve this issue, the first step you should take is to clear your cache, which means clearing your browser history or opening ChatGPT in incognito mode to test if the Enter key works there.
If the Enter key functions properly in incognito mode, then you should try clearing your chat history and testing again.
Also read: Why you should use ChatGPT every time when you write your cover letter?
Various browser extensions can also potentially cause this disruption. If you are using any extensions, you should disable them and try again.