As the title says, LibreOffice has frozen and I can't do anything. Sadly I don't want to force exit because of the document. Are there any tricks or can you rely on restore?
If the process is stuck or has been frozen you cannot do anything except waiting for it to continue or force quit the process.
If there was any other option available the applications which get frozen would do this themselves already by default. I'm sorry if this answer doesn't satisfy you, but I've faced the same issues myself. Please note that applications with a restore option will show you this after the force quit and restart.
If you don't know this: Try creating a screenshot to save the visible part of your file.
If it's frozen, you will need to Force Quit it. If the app is enabled for Restore, the document should be fine when you relaunch the app.