$ grep ^[^#] /etc/apt/sources.list /etc/apt/sources.list.d/*
/etc/apt/sources.list:deb http://deb.devuan.org/merged daedalus                  main non-free-firmware non-free contrib
/etc/apt/sources.list:deb http://deb.devuan.org/merged daedalus-updates          main non-free-firmware non-free contrib
/etc/apt/sources.list:deb http://deb.devuan.org/merged daedalus-security         main non-free-firmware non-free contrib
/etc/apt/sources.list:deb http://deb.devuan.org/merged daedalus-proposed-updates main non-free-firmware non-free contrib
/etc/apt/sources.list:deb http://deb.devuan.org/merged daedalus-backports        main non-free-firmware non-free contrib
/etc/apt/sources.list.d/josm.list:deb https://josm.openstreetmap.de/apt/ alldist universe

php8.2-cli : Depends on: php8.2-common (= 8.2.7-1~deb12u1) but versione 8.2.15-1+0~20240120.39+debian12~1.gbp56f296 is goingto be installed 

and it stops...

@alexkemp
could you please provide your sources.list ?

I wonder whether has anybody successfully installed php on Daedalus

Er, yes (though not for a website)

$ apt search php | fgrep -i installed

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

php-cli/stable,now 2:8.2+93 all [installed]
php-common/stable,now 2:93 all [installed,automatic]
php-mbstring/stable,now 2:8.2+93 all [installed]
php8.2-cli/stable,stable-security,now 8.2.7-1~deb12u1 amd64 [installed,automatic]
php8.2-common/stable,stable-security,now 8.2.7-1~deb12u1 amd64 [installed,automatic]
php8.2-mbstring/stable,stable-security,now 8.2.7-1~deb12u1 amd64 [installed,automatic]
php8.2-opcache/stable,stable-security,now 8.2.7-1~deb12u1 amd64 [installed,automatic]
php8.2-readline/stable,stable-security,now 8.2.7-1~deb12u1 amd64 [installed,automatic]

With php8.3 & C. in a not complete installed status, now every try to install anything reports error in php8.3-cli etc, throws error.
I tried to install php8.2 from merged repos, but dpkg shows the same error for php8.2-cli as for php8.3-cli

(dpkg: errore nell'elaborare il pacchetto php8.2-cli (--configure):
 il sottoprocesso installato pacchetto php8.2-cli script post-installation ha restituito lo stato di errore 1

The whole system, although still running looks to be inconsistent.

At this point I wonder whether has anybody successfully installed php on Daedalus...

apt-get install --reinstall libc6

But be sure to have a rescue boot at hand, just in case, because it's a rather fundamental system transition. Otoh it should have happened on the upgrade... did you "dist-upgrade" at all?

https://packages.sury.org.

I'm wondering if this third-party repository has packages that aren't Devuan compatible for whatever reason.

At your own risk you could try removing that symbollic link and installing php8.3 from Debian Experimental.

/usr/lib/x86_64-linux-gnu/libc.so.6 -> libc-2.31.so

is recreated every time I update/install packages. I found that because updating php8.3 from https://packages.sury.org.

The system can't install php8.3-cli :
removed bad link, linked libc.so.6 to the right file as above, ldconfig, run dpkg -i package (I also tried apt before), then I get :

(Lettura del database... 100266 file e directory attualmente installati.)
Preparativi per estrarre php8.3-cli_8.3.2-1+0~20240120.16+debian12~1.gbpb43448_amd64.deb...
Estrazione di php8.3-cli (8.3.2-1+0~20240120.16+debian12~1.gbpb43448) su (8.3.2-1+0~20240120.16+debian12~1.gbpb43448)...
Configurazione di php8.3-cli (8.3.2-1+0~20240120.16+debian12~1.gbpb43448)...
expr: /usr/lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.34' not found (required by expr)
dpkg: errore nell'elaborare il pacchetto php8.3-cli (--install):
 il sottoprocesso installato pacchetto php8.3-cli script post-installation ha restituito lo stato di errore 1

then,

find /usr/lib* /lib* -name libc.so\* | xargs ls -l
-rwxr-xr-x 1 root root 1922136 30 set 10.31 /lib/x86_64-linux-gnu/libc.so.6
-rw-r--r-- 1 root root     283 30 set 10.31 /usr/lib/x86_64-linux-gnu/libc.so
lrwxrwxrwx 1 root root      12 21 gen 12.50 /usr/lib/x86_64-linux-gnu/libc.so.6 -> libc-2.31.so

something recreated the wrong link...

I think the installation script of php8.3-cli is messing up something...

As always, the most weird things happen to my server. Note that I first migrated from Bullseye to Chimaera, and then I upgraded to Daedalus. The error appeared after upgrading to Daedalus, I'm quite sure it didn't show up before. It would be interesting to understand what happened exactly, but for the moment I'm happy that it has been solved. Thank you very much again.

# ldconfig

which usually does good things to the libraries. You might also need to set a new link (as root)

# ln -sTf /lib/x86_64-linux-gnu/libc.so.6 /usr/lib/x86_64-linux-gnu/libc.so.6

to sort out that dangling one.

I would think this all has to do with system differences between bullseye and daedalus (bookworm), and yet it's peculiar that only expr brings a problem.