Before EJS version 4.2, the default file extension for ejs is "xml".
It has been changed to "ejs" since EJS 4.3
When you create a new ejs simulation and save it, you can just type the filename.
And EJS will save the file with extension ".ejs".

However, if you open previous simulation source where the extension is "xml".
Then, EJS will not change the extension so that previous version can be run as well.

If you really want to save the file with extension "ejs", then you can type the full filename (filename + extension".

May I know why you want the source to become "ejs" type?