Comment 2 for bug 1950794

Turns out dropping "debian/patches/units-Don-t-start-systemd-udev-trigger.service-in-a-conta.patch" (that we want to drop anyway) makes a difference here, i.e. removing the "ConditionVirtualization=!container" line from /usr/lib/systemd/service/systemd-udev-trigger.service.

# apt install systemd udev # upgrade systemd & udev to v249
# systemctl restart systemd-udev-trigger # run the 'udevadm trigger' commands
# systemctl restart systemd-networkd # restart networkd to re-run the DHCPv4 client.

That is even though the systemd-udev-trigger.service fails to execute successfully:
# systemctl status systemd-udev-trigger.service
● systemd-udev-trigger.service - Coldplug All udev Devices
     Loaded: loaded (/lib/systemd/system/systemd-udev-trigger.service; static)
     Active: active (exited) since Wed 2021-11-17 09:39:01 UTC; 37s ago
       Docs: man:udev(7)
             man:systemd-udevd.service(8)
    Process: 74 ExecStart=udevadm trigger --type=subsystems --action=add (code=exited, status=1/FAILURE)
    Process: 101 ExecStart=udevadm trigger --type=devices --action=add (code=exited, status=1/FAILURE)
   Main PID: 101 (code=exited, status=1/FAILURE)
        CPU: 160ms

Nov 17 09:39:01 jj2 udevadm[101]: nvme-delete-wq: Failed to write 'add' to '/sys/devices/virtual/workqueue/nvme-delete-wq/uevent': Permission denied
Nov 17 09:39:01 jj2 udevadm[101]: nvme-reset-wq: Failed to write 'add' to '/sys/devices/virtual/workqueue/nvme-reset-wq/uevent': Permission denied
Nov 17 09:39:01 jj2 udevadm[101]: nvme-wq: Failed to write 'add' to '/sys/devices/virtual/workqueue/nvme-wq/uevent': Permission denied
Nov 17 09:39:01 jj2 udevadm[101]: raid5wq: Failed to write 'add' to '/sys/devices/virtual/workqueue/raid5wq/uevent': Permission denied
Nov 17 09:39:01 jj2 udevadm[101]: scsi_tmf_0: Failed to write 'add' to '/sys/devices/virtual/workqueue/scsi_tmf_0/uevent': Permission denied
Nov 17 09:39:01 jj2 udevadm[101]: writeback: Failed to write 'add' to '/sys/devices/virtual/workqueue/writeback/uevent': Permission denied
Nov 17 09:39:01 jj2 udevadm[101]: dm-0: Failed to write 'add' to '/sys/devices/virtual/block/dm-0/uevent': Permission denied
Nov 17 09:39:01 jj2 udevadm[101]: dm-1: Failed to write 'add' to '/sys/devices/virtual/block/dm-1/uevent': Permission denied
Nov 17 09:39:01 jj2 udevadm[101]: dm-2: Failed to write 'add' to '/sys/devices/virtual/block/dm-2/uevent': Permission denied
Nov 17 09:39:01 jj2 udevadm[101]: dm-3: Failed to write 'add' to '/sys/devices/virtual/block/dm-3/uevent': Permission denied