@Nikita-Zhavkin Make sure you have installed the "More Tracks and Formats" feature from the store to be able to export as MP3. Alternatively you can export as WAV and use a free converter like XMedia Recode to convert your file to MP3.
@SP. How do we install or check to see if "More Tracks & Formats" is installed? And why was I able to open and save as MP3 on my previous laptop and not new one? :-/
@Singing-Phillip Usually it gets automatically unlocked after you log in with your user acoount. You need to be logged in or it won't work. If it still doesn't work then you can open the program settings and click on the button to clean up the store.