Both .enex and .enb files are databases from Evernote, with the key difference that ENEX are the newer one. While it is possible to convert older databases to newer format with the tool provided by Evernote, the opposite is very unlikely. If you for some reason need this, perhaps it would be best to contact Evernote support or forums and see if they have solutions for this problem.
Updated: July 19, 2023