After https://git.libreoffice.org/core/+/35c93c5f8e40dff4819849b240044cd9d99221a0%5E%21 Document autofill improvements. Ref: terse notice in https://wiki.documentfoundation.org/ReleaseNotes/24.8#Calc
Got this reply now: The improvement is actually "making AutoFill work by calling it explicitly with Uno commands". AutoFill was only working with mouseUp events, but now this is changed, we can also use it without relying on mouse events. It does not change/add any visible improvement on the UI, it is just a small improvement. We already have copy-cells by ctrl-dragging & fill-series by dragging, those behaviors were not changed.