On my fresh #Debian 12 server:

# cat /var/log/README
You are looking for the traditional text log files in /var/log, and they are
gone?

Here's an explanation on what's going on:

You are running a systemd-based OS where traditional syslog has been replaced
with the Journal. The journal stores the same (and more) information as classic
syslog. To make use of the journal and access the collected log data simply
invoke "journalctl", which will output the logs in the identical text-based
format the syslog files in /var/log used to be. For further details, please
refer to journalctl(1).

Alternatively, consider installing one of the traditional syslog
implementations available for your distribution, which will generate the
classic log files for you. Syslog implementations such as syslog-ng or rsyslog
may be installed side-by-side with the journal and will continue to function
the way they always did.

Thank you!

Further reading:
        man:journalctl(1)
        man:systemd-journald.service(8)
        man:journald.conf(5)
        https://0pointer.de/blog/projects/the-journal.html

#systemd