[Off-Topic] How installing a package in emacs broke KDE on my system, can't login now

[dexcy]

After installing a pdf-tools package inside emacs and writing (pdf-tools-install) in init.el, emacs offered me at launch to recompile some epdfinfo package. I let it rebuild it, thinking, "what can go wrong"? In the end of a relatively long (5 min or so) compilation process in which, if I understand correctly, dpkg reconfigured, upgraded, removed, reinstalled all sorts of system packages (lib- apparently needed for poppler which is needed for epdfinfo?), things related to qt and KDE like sddm, plasma it even deleted konsole in the process (wtf). Perhaps this is due to the fact that I have not updated the system for a long time (a couple of years, probably, Debian 12-based Kali, just not the main machine I occasionally use for study) and there was a lot of new dependencies, idk, maybe it was the reason. Anyway, after this recompilation, dpkg (I think) offered to restart 18 services, including sddm and some more, well, I thought, why not ... and after that the system shuts down and no longer boots.

With the login I see the following:

"The current cannot be loaded to give to errors below, please select another theme"
"file://usr/share/sdre/sddm/themes/breeze/Main.qml no such file or directory"

When I try to enter the password and press the Enter, nothing just happens. At least I can switch to a different tty, though

Of the probably relevant logs in /var/log/dpkg.log:

status installed <package>
status half-installed <package>
status half-configured <package>
status configured <package>
status unpacked <packet>

Many logs of this type with appropriate timestamps of the time dpkg was doing it.

What can be done to fix it or rollback as it was without making it worse? Never really had to fix anything related to KDE and such a large-scale dpkg mess-up.

Also, I don't think the problem is merely with sddm. I suspect my emacs package installation was merely a catalyzer for a long-standing problem with dependencies due to lack of updates (I've seen suspicious suggestiong by dpkg before as well, like when it suggested to install/upgrade/remove hundreds of packages, including system ones like konsole in order to install some innocent little package).

It does seem that in /var/backups I have some automatic backups like dpkg.status.0 and apt.extended_states.0 from a few days ago, and in /var/log/syslog a few hours before today's disaster there's a log of dpkg.db.backup-service, though I haven't found where it stores these backups yet, and what I can actually restore with them, and whether it can accurately fix my problem or not.

Also, here's the package that kickstarted everything:

https://elpa.nongnu.org/nongnu/pdf-tools.html

pdf-tools requires a server epdfinfo to run against, which it will try to compile and build when it is activated for the first time.

...

This rendering is performed by a special library named, for whatever reason, poppler, running inside a server program. This program is called epdfinfo and its job is to successively read requests from Emacs and produce the proper results, i.e. the PNG image of a PDF page.