Edge does not let you customize the new tab page. The new tab page always opens a custom Bing page, and Edge extensions do not work on this page. 

This extension lets you point the new tab page to a URL of your choice. It can be Bing.com, your company's homepage, or a blank page. It is lightweight on your browser (<50kb - compared to, for example, Grammarly, which is 36MB), has no tracking, and is straightforward to use.

Some popular choices:
1) Bing - https://www.bing.com
2) Google - https://google.com
3) Voice In Notepad - https://dictanote.co/voicein/notepad/
4) ChatGPT - https://chat.openai.com
5) Blank Page - about:blank

You can also set it to a local file path like file:///C:/Documents/test.html . You can set the URL to an internal page like edge://apps too.

Customization:
1) Focus on the address bar on the new tab page: When checked, the focus and cursor are in the address bar when you open a new tab page. When unchecked, the focus is on the page. 

If you want to disable the custom new tab extension, you can do so by going to edge://extensions and disabling this extension.