I would suggest trying this app: https://open-store.io/app/logviewer.ruditimmer, which simplifies the access to logs using kjournald as a backend.

I of course use this very good and essential app which does the work automatically.

Thank you for your explanation which clarifies a little in my head.

Generally these logs are stored in /var/log/journal (which a quick Googling will reveal), however the whole toolkit is quite different to what we used to have before so unfortunately you can't even expect the same from it.

I would suggest trying this app: https://open-store.io/app/logviewer.ruditimmer, which simplifies the access to logs using kjournald as a backend.

Regarding the journal, this might come handy: https://wiki.archlinux.org/title/Systemd/Journal

What would you like to do ?

Nothing in particular. Just know where the logs are stored. It was 'upstart' under Xenial.

@lduboeuf Thanks but I don't know how to use and analyze the result of this command. I would like to know if there is a specific logs directory somewhere like 'upstart' please. If so, what is the path?

The log viewer (focal) I'm using doesn't seem to give me a path in parameters. Maybe it's normal but i would like to understand why. Thanks again.

journalctl is common on many linux system, it stores logs in /var/log/journal but hard to find things there, instead all can be done with journalctl command and you can find lots of resources on the Internet how you can use it.
What would you like to do ?

The log viewer (focal) I'm using doesn't seem to give me a path in parameters. Maybe it's normal but i would like to understand why. Thanks again.