for this important plugin! I love the feature that each highlight has a link to open up the book in Calibre and to scroll to the exact location of the highlight!
What follows are some suggestions to improve your plugin:
To get better control of sending highlights to Obsidian, I suggest adding the option "Send Highlights of Selected Books to Obsidian". This would confine sending the highlights only of selected books in the Calibre library.
In addition, of the highlight's timestamp, I would need as a sort-key the location of the highlight in the book: Highlights in the first chapter appear before highlights in the second chapter, even if chapter one was later highlighted than chapter two.
The time when highlights were sent does not reflect my local time (UTC + 1). I had to set it manually one hour earlier to get only the latest highlights.
Provide an image (the Obsidian logo?) for the H20 button in the toolbar to get a nicer view in the UI.
Your plugin does not appear in the list of Calibre plugins, even after the installation via the file upload. (Calibre Config -> Advanced Plugin -> Get new plugins).