I really don’t know that we’ve had to explain before how to recover data from the special backup files that Notepad++ creates.
The WORST way is what the OP has done above – opening and continuing to edit a “new 2@yyyy-mm-dd_hhmmss” file directly.
Another bad way to do it would be to create a new “new 2” tab and the open “new 2@yyyy-mm-dd_hhmmss” briefly, only long enough to copy its data out and paste into the “new 2” tab, and continuing to work on that “file”.
The best way, as Peter hints, is to create a new tab and paste the data there, then IMMEDIATELY save it as a hard-named file in the file system, i.e., don’t let it sit there as “new 2” again (opening yourself up to the original problem recurring).