Drag drop into booklist working fine here, I'm running same version of windows 10, with the same recent updates.
Are you running calibre as Administrator, see penultimate para in ==>>
https://manual.calibre-ebook.com/faq...ror-on-windows.
Also try safe mode, could be a 3rd party tool, or shell extension.
BR
Oh,yes - the slashed circle cursor is generated by Windows as a result of how applications respond to Drag Over events. I see a slashed circle as I drag a file over the Tag browser, it changes to a Copy+ when I reach the book list window.
Another thing I'm wary of is file managers that have a "Replace File Explorer" feature. I use xplorer˛, but I would never enable that feature.