This blog entry shows a couple of last-minute changes, but I haven't found any release notes yet. However, here is a list of development hightlights blog posts [0] and the 6.0.0-rc1 milestone page [1].

[0] https://www.kicad.org/blog/categories/Development-Highlight/

[1] https://gitlab.com/groups/kicad/libraries/-/milestones/1#tab...