Looks to me like calibre is expecting to find a device, and there isn't one. I'm no expert at the device features of calibre, but I thought one had to explicitly tell it to Connect to a device/folder before it would start looking for one.
If you deleted your library via your file manager then you will need to Remove it from calibre. And then you'll need to create a new library in calibre.
IMO it's only then you should attempt to Connect your device or add books. I don't think calibre 'likes' not having a database on which to operate.
BR
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