I would clean-up drastically, and then reinstall the stuff (again).
Purge gnome, install a simple DM.

apt install slim task-gnome-desktop-  --purge --auto-remove   ## there is a "-" after desktop 

Does the remaining xfce work?
if not purge it too, which should leave just the text console.

apt purge task-xfce-desktop slim --auto-remove

Be careful:
apt with option "-s" additionally runs a simulation.
Take care of the network, if you are using something else than dhcp.
"purge" will delete the (system-)config files too, when removing.

Edit: typo

That is a good question for Intel.

As written before, you may want to use uuids or labels to identify partitions.

apt will not downgrade a package versions, unless you pin it.

Or it was a bug:

I got the same installation and error respective ntp on my pc.
Beside the fail-message, ntpd was actually running (ps ax | grep ntpd).
The final fix in my case was: apt purge ntp. EDIT: To have ntp in any case, additionally: apt install ntpsec

Description:
There were two init.d-scripts existing, both return "fail" on "status".
/etc/init.d/ntp
/etc/init.d/ntpsec
After doing apt purge ntp, the file /etc/init.d/ntp was gone and /etc/init.d/ntpsec status now returns correctly "running".
Re-installing for testing purposes: apt install ntp did not harm anymore, it turned into a basically empty (meta-)package. I don't remember the exact content, but ntp was a "real" package with functionality.

Summary / assumption: package ntp was not upgraded corectly by the new metapackage. The (installed file-)content changed after de- and re-installing it.

I don't think it is "bug 700".
700 does not harm, it is an unhappy apt, complaining about an unfinished package installation, which functionally succeeded. Anything else is in order.
The error message looks like something went wrong with nvidia-persistenced.

What about the 2 not upgraded packages?
Just hoping that apt upgrade or dist-upgrade might fix it.
And de-installation is an option too.

To complete #2:
I never tried to boot the kernel with the error during module compilation, just returned to daedalus' 6.1.
And there is a nvidia card involved as well, using the current driver version.

There can be only ONE grub in the MBR.
Booting the respective installation and doing update-grub (or aquivalent command) should find the new installed devuan and make a boot-entry for it.

# apt install sysvinit-core 
# reboot

and init is pid 1.

Usually not.

$ sudo apt purge nvidia-persistenced

It took me a lot of time to come to that point.

Or, if you want to keep it:

$ sudo /etc/init.d/nvidia-persistenced stop
$ sudo apt install 

Then apt should be happy again.

The point on appimage is to have no dependencies.

Try the big one - the small one is a broken, it has the mentioned dependency.

I would
(1) invest in a new small SSD - just 20 bugs, it's worth it.
(2) use the the nvidia drivers from the non-free devuan repo (not the installer offered by nvidia)
(3) sysV-init is default

The counterpart to debian bookworm is devuan daedalus (but not yet released as new stable), the current stable release is still chimaera.

The title includes "dual-boot" and "best method".

20 bugs for an addional SSD - it's worth it.

One operating system per physical drive is a clear approach.
Installations can be done in a way that each drive can boot its operating system independently.
Since only one drive can boot as default, other drives may be selected through the "BIOS boot menu" ([F12] on my computer).
But grub can detect and start most operating systems anyway.