There’re situations when it’s not enough to have documents in a single library, you might need to share a copy with your colleagues, create a backup elsewhere or just archive the old files to a different library.
Do you need to copy files in SharePoint but prefer the Classic layout? Or do you need to copy the files between SharePoints in different organisations?
Do you need to copy files in your Modern SharePoint?
“Take the SharePoint document library id from the url“ is the most common answer, but from where exactly and how?”