https://unix.stackexchange.com/questions/709570/how-to-keep-systemd-journal-for-one-year
this should do
#How do I backup systemd journal logs?
12 messages · Page 1 of 1 (latest)
they also are in /run/log, these get wiped everytime you reboot
you should be able to specify some other directory/device in the configuration file
I recommend to read the link in that article (https://www.freedesktop.org/software/systemd/man/latest/journald.conf.html)
it explains everything, may be a bit complicated though
install ksystemlog done.