New virtualbox version 7.2.12 r 174389 (Qt6.8.0) will boot user session to black screen, sysmaint working fine.
Looking at this:
VirtualBox→click a VM→Settings→Display→Graphics Controller→increase slider for Video Memory to 128→OK(This is already the default in recent releases of Kicksecure.)
Resolves manually created KS VM which doesnt come with 128 MB by default when created by vbox (only 16 MB).
Another solution which resolved Whonix user session, reboot Windows.
Both worked fine after that.