It's recommended to regularly backup the song library; you might need to reset your computer, hardware failures or reinstall the app etc.

In iReal Pro, click the Settings icon (at the top of the Library),
Settings icon image scroll down Settings and click on Backup Songs and Playlists.

A backup file will be created and Windows will automatically save it into your Windows Downloads folder. A brief message from Windows indicates what it has done, Click Show in folder to find your file.

MS message, option buttons to Open file or Show in folder

(You might like to store a copy in OneDrive (or similar), move it to your Documents folder or email it to yourself as your Downloads folder may not be automatically backing up to OneDrive. This is a precaution to keep your files safe.)