How to uninstall a package from Debian backports (not a duplicate Q)

I know there are a few Questions here which ask the same question I appear to be asking. I have tried those suggestions (https://unix.stackexchange.com/a/439342/286615) & (https://unix.stackexchange.com/a/151371/286615) , but they do not work in this case. Here's what has happened:

pi@raspberrypi0w:~ $ sudo apt -t bullseye-backports install udev
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following additional packages will be installed:
  libudev1
The following packages will be upgraded:
  libudev1 udev
2 upgraded, 0 newly installed, 0 to remove and 35 not upgraded.
Need to get 1,654 kB of archives.
After this operation, 511 kB of additional disk space will be used.
Do you want to continue? [Y/n] Y
Get:1 http://deb.debian.org/debian  bullseye-backports/main armhf udev armhf 252.5-2~bpo11+1 [1,554 kB]
Get:2 http://deb.debian.org/debian  bullseye-backports/main armhf libudev1 armhf 252.5-2~bpo11+1 [100 kB]
Fetched 1,654 kB in 1s (1,267 kB/s)
Reading changelogs... Done
(Reading database ... 43648 files and directories currently installed.)
Preparing to unpack .../udev_252.5-2~bpo11+1_armhf.deb ...
Unpacking udev (252.5-2~bpo11+1) over (247.3-7+rpi1+deb11u2) ...
Preparing to unpack .../libudev1_252.5-2~bpo11+1_armhf.deb ...
Unpacking libudev1:armhf (252.5-2~bpo11+1) over (247.3-7+rpi1+deb11u2) ...
Setting up libudev1:armhf (252.5-2~bpo11+1) ...
Setting up udev (252.5-2~bpo11+1) ...
Segmentation fault
Job for systemd-udevd.service failed because a fatal signal was delivered to the control process.
See "systemctl status systemd-udevd.service" and "journalctl -xe" for details.
invoke-rc.d: initscript udev, action "restart" failed.
● systemd-udevd.service - Rule-based Manager for Device Events and Files
     Loaded: loaded (/lib/systemd/system/systemd-udevd.service; static)
     Active: activating (start) since Tue 2024-04-09 07:36:27 UTC; 130ms ago
TriggeredBy: ● systemd-udevd-control.socket
             ● systemd-udevd-kernel.socket
       Docs: man:systemd-udevd.service(8)
             man:udev(7)
   Main PID: 8773 ((md-udevd))
      Tasks: 1
        CPU: 45ms
     CGroup: /system.slice/systemd-udevd.service
             └─8773 (md-udevd)

Apr 09 07:36:28 raspberrypi0w systemd: Stopped Rule-based Manager for Device Events and Files.
Apr 09 07:36:28 raspberrypi0w systemd: Starting Rule-based Manager for Device Events and Files...
Apr 09 07:36:28 raspberrypi0w systemd: systemd-udevd.service: Main process exited, code=killed, status=11/SEGV
Apr 09 07:36:28 raspberrypi0w systemd: systemd-udevd.service: Failed with result 'signal'.
Apr 09 07:36:28 raspberrypi0w systemd: Failed to start Rule-based Manager for Device Events and Files.
Apr 09 07:36:28 raspberrypi0w systemd: systemd-udevd.service: Scheduled restart job, restart counter is at 5.
Apr 09 07:36:28 raspberrypi0w systemd: Stopped Rule-based Manager for Device Events and Files.
Apr 09 07:36:28 raspberrypi0w systemd: systemd-udevd.service: Start request repeated too quickly.
Apr 09 07:36:28 raspberrypi0w systemd: systemd-udevd.service: Failed with result 'signal'.
Apr 09 07:36:28 raspberrypi0w systemd: Failed to start Rule-based Manager for Device Events and Files.
dpkg: error processing package udev (--configure):
 installed udev package post-installation script subprocess returned error exit status 1
Processing triggers for libc-bin (2.31-13+rpt2+rpi1+deb11u8) ...
Processing triggers for man-db (2.9.4-2) ...
Processing triggers for initramfs-tools (0.140) ...
Errors were encountered while processing:
 udev
E: Sub-process /usr/bin/dpkg returned an error code (1)

The attempted "reversion" wasn't very interesting:

pi@raspberrypi0w:~ $ apt install ${udev}/bullseye
Illegal instruction

I attempted a few other "reversions":

pi@raspberrypi0w:~ $ sudo apt install udev
Illegal instruction
pi@raspberrypi0w:~ $ sudo apt-get install udev/stable
Illegal instruction
pi@raspberrypi0w:~ $ sudo apt-get install udev/old-stable
Illegal instruction

A 'segmentation fault' - sounds serious :). I was unsure what this meant; i.e. did the system automatically reject the udev upgrade & revert automatically? - or have I stepped in it? I waited a few minutes & tried this:

$ systemctl status systemd-udevd.service
● systemd-udevd.service - Rule-based Manager for Device Events and Files
     Loaded: loaded (/lib/systemd/system/systemd-udevd.service; static)
     Active: failed (Result: signal) since Tue 2024-04-09 07:36:28 UTC; 28min ago
TriggeredBy: ● systemd-udevd-control.socket
             ● systemd-udevd-kernel.socket
       Docs: man:systemd-udevd.service(8)
             man:udev(7)
    Process: 8776 ExecStart=/lib/systemd/systemd-udevd (code=killed, signal=SEGV)
   Main PID: 8776 (code=killed, signal=SEGV)
        CPU: 199ms

Apr 09 07:36:28 raspberrypi0w systemd: systemd-udevd.service: Scheduled restart job, restart counter is at 5.
Apr 09 07:36:28 raspberrypi0w systemd: Stopped Rule-based Manager for Device Events and Files.
Apr 09 07:36:28 raspberrypi0w systemd: systemd-udevd.service: Start request repeated too quickly.
Apr 09 07:36:28 raspberrypi0w systemd: systemd-udevd.service: Failed with result 'signal'.
Apr 09 07:36:28 raspberrypi0w systemd: Failed to start Rule-based Manager for Device Events and Files.

I have a good (image) backup from last night, so if I've killed my OS I can recover. However, I'd prefer to fix this without resort to the backup - if that's possible. What should I do?