You should note that line breaks are implemented using different characters in different environments.
For example, in the input box (this is the case when submitting in your question) or in a text file or on the terminal,
indicates a new line using the control character "nr" or "n" or "r" (refer to the constant PHP_EOL).
In a browser environment (this is the case with the front-end mentioned in your question), line breaks are implemented by the "<br />" tag.
So, when outputting, you need to convert "nr" or other line breaks into line break tags in the HTML language.
Usually, the easier solution is the nl2br() function.

nl2br()

For details, please visit Baidu or view the official php documentation

Use pre tag to wrap the content when displaying

https://developer.mozilla.org...

1. Use rich text box

2. will be converted to newline character in js:

var text= 'aaa bbb ccc';
text = text.replace("\n\r", "<br/>");