If you’re on a Windows PC oftentimes you can go to the user temp folder and find the working document there. %temp% in file explorer.
You might have to do a little digging to find out what/where it is, sometimes they’re nice and obvious in a folder named for the app creating it, sometimes it’s a string of nonsensical alphanumeric characters.
Also: You can go to the “Tools” followed by “Options” then go to “LibreOffice” and click on “Path”, temp and backup files are stored at the location listed there, too.
Either way, I highly, highly suggest you dig around for the lost doc in that folder. It’s saved my butt a couple times when I forgot to save.
Good luck.