There is nothing listed in Known Issues and Solutions in the 2024-11-30 Stable Update announcement you referenced.
The item Plasma 6.2 might create a black screen when using X11 and default theme mentions a “black lock screen when using Breeze Plasma style, but controls are all there and remain interactive” but that’s not what was described here.
The report on KDE Discuss (linked previously) is a match for the OP’s issue, which in turn is possibly related to KDE bug #497806
Nonetheless, thank you for your input.