Are you confusing a Virtual Library (a subset) with a real Library?
Every Real Library has a
metadata.db in its folder (plus author folders). The containing folder is the Library Name.
If you only find 1 folder with
Metadata.db:
1)and you see Author folders, but no DB, then the Library has been Damaged and needs to be rebuilt following the tips in the FAQ
2)You cant even find the author folders:
a) The drive was removable or is off-line (blocked?).
b) You failed to heed FAQ advice and used a cloud or Network drive that has become unavailable. Working Library on Local drives only. Backups any place
as long as they are not active during Library use.
c)The Library (folder)has been DELETED at the OS (or your file system rights were removed)
(I remember someone had the Library folder on the desktop (not a shortcut) and the desktop got
cleaned 