Wow thanks for the quick reply and clarification again.
I've got Kindle Mate installed. Kindle Mate does not provide the solution I'm looking for, but provides a good method for backing up the content - as I understand it.
But since I want to have the saved highlights and annotations in the cloud
together with the book or better said to view them in the book itself (for better context, etc) - I'm faced with the dilemma of having used and saved my books so far in azw3 format (included generating the correlative azw3r and azw3f metadata files) which I cannot use to restore my annotations and highlights if I send them to the device as mobi or azw.
It looks like I'll have to select my most worked-on and important books, send them via email to kindle as .mobi, open
www.clippings.io with my saved annotations and highlights and restore the clippings manually... If it's not tooo time consuming.
But in the future, I'll definitely send new books via .mobi for sure and simply use WhisperSync across all devices!
Thanks again for the prompt replies and trying to understand what it is I'm looking for ^^