After going from HTML to visual, it clears the code

<xmp> was deprecated in HTML 3.2 and is now obsolete.

Oh thanx.

Is there another way to view long HTML code as text?
Without having to replace the character after the character?

Didn’t you use it in your question?
<code>HTML code or PHP code or JS code...</code>

<code> </code> does not stop rendering HTML code in web browser.
I tried.

https://codepen.io/Ogi22/pen/XxGBvz

• This reply was modified 6 years, 1 month ago by ogi22.
• This reply was modified 6 years, 1 month ago by ogi22.

I see. I was thinking that the < and > characters got converted, but they do not.

Well, the editor keeps it when I use <xmp>, so it might be that your user does not have unfiltered_html capability, or that the filters have changed since version WP 4.7.11 (which is what my test site is running).
Edit: But you really should not use deprecated HTML tags. There does not seem to be an equivalent, because <pre> and <code> still interpret the HTML, so you have to change all the characters yourself. It might be better for you to use a syntax highlighter plugin.