Thank you! They recovered all my files and reinstalled something they called "MacOS", no clue what that is, but apparently it's important on Apple Book Computer. They also told me that the command line is dangerous to use, even though I use it all the time, since it reminds me of MS-DOS.
Apparently, since the Apple Computer folks are American they call it "trash" not "bin", so I have to delete /trash/ from now on!