I posted some findings at After recent update, Windows HVM can no longer network through Whonix gateway · Issue #9990 · QubesOS/qubes-issues · GitHub
Workaround in sys-whonix:
echo 1 | sudo tee $(find /proc/sys/net/ipv4 -name arp_ignore)
(this won’t persist restart, needs to be repeated after each sys-whonix start)
Can you find approximately which update broke it? Especially what was the working version of the security-misc package