Sillily (LOL) I tried a Dist Upgrade (Linux MX dist upgrade
from Wildflower to Libretto) without following exactly the
procedure in the MX 23 Forum
here :
https://mxlinux.org/wiki/system/upgrading-from-mx-21-to-mx-23-without-reinstalling/
I resume the steps below
Upgrade Steps:
1) Upgrade your system to the latest packages with:
sudo apt update; sudo apt full-upgrade
2) Install mx23-archive-keyring:
sudo apt install mx23-archive-keyring
3) Change sources to point to bookworm release (search
all .list files and replace “bullseye” with “bookworm”):
find /etc/apt -name "*.list" -exec sudo sed -i
's/bullseye/bookworm/g' {} +
4) Add non-free-firmware to debian sources (or by hand:
edit the debian.list and add “non-free-firmware” to each deb
line):
grep -qF 'non-free-firmware'
/etc/apt/sources.list.d/debian.list || sudo sed -i
's/non-free/non-free non-free-firmware/g'
/etc/apt/sources.list.d/debian.list
5) Upgrade packages (make sure nothing important is
removed at this step: examine the prompt before you press “y”):
sudo apt update; sudo apt full-upgrade

Now, acting sillily basing on what I recalled, I performed
all stages FORGETTING 2) Install mx23-archive-keyring:

The upgrade resulted in PARTIAL success (and failure
overall). I dunno exactly what was upgraded and what not.
I then, late alas, to do step 2) afterwards, but then the
package mx23-archive-keyring was no longer available.
Maybe it belonged to the ORIGINAL MX21 Repo, that had been
overwritten by hand.
Am I right ?
Is it still a way (I tried using WGET, failing, as unable to
locate the correct package name, which apparently is neither
mx23-archive-keyring nor mx23-archive-key or suilar, and
moreover the URL could be wrong too or both), but well, as I
was saying : Is it still a way to install a single package
from a given repo (the original WILDFLOWER 21 Repo) in the
new system, and then repeat the upgrade procedure ?
Some core package, resulting NOT SIGNED, refuse to be
upgraded, so such keys are necessary.
I hope I was able to explain sufficiently sth I don't
understand myself.
Tnx for any advice for this mess (the system runs, and
reports itself as the OLD one, even if it upgraded many
hundreds of packages)

--
1) Resistere, resistere, resistere.
2) Se tutti pagano le tasse, le tasse le pagano tutti
MarioCPPP