@sealdeer Sorry to hear about this. We can only offer you to upload your file on this link so we can try to recover whatever was saved.
It’s quite possible the first frames weren’t saved depending how the problem occurred, as this happens when saving / packaging the file.
If you have a previous file please use that to finalize recovering your work, otherwise please follow this guide and see if it’s even remotely possible to recover the files that are dumped to the temporary file of your operating system:
Either way, there is a high chance that you have to at least redo your work partially, so please download the latest verson available of Pencil2D and try saving either various backup copies of your work or use the PCL file type which does not save to a single file but to a folder with all the components, and that way it will be a bit harder to lose work (but don’t forget to still save copies of that!)
Edit: By the way when sharing the Pencil2D file make sure you don’t mark the “Make my work public” checkbox so only the developers can see it