Hi! I'm a new Ubuntu user (I'm just starting out), and after spending hours and hours configuring my system, I noticed that my PC was taking much longer to shut down (not even 5 seconds at first, compared with over two minutes now). I asked some AIs, and they advised me to use the following command to list the various errors since my last boot: journalctl -rb 0 -p 0..3
Here's the output I got:
mars 25 20:12:17 gybbs gdm-launch-environment][895]: GLib-GObject: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
mars 25 20:12:15 gybbs systemd[1396]: Failed to start Application launched by gnome-session-binary.
mars 25 20:12:15 gybbs systemd[1396]: Failed to start Application launched by gnome-session-binary.
mars 25 20:12:15 gybbs systemd[1396]: Failed to start Application launched by gnome-session-binary.
mars 25 20:12:14 gybbs gdm-password][1379]: gkr-pam: unable to locate daemon control file
mars 25 20:10:52 gybbs pulseaudio[948]: Module module-bluetooth-discover not loaded.
mars 25 20:10:52 gybbs pulseaudio[948]: Module module-bluetooth-policy not loaded.
mars 25 20:10:52 gybbs gnome-session-binary[980]: GLib-GIO-CRITICAL: g_bus_get_sync: assertion 'error == NULL || *error == NULL' failed
mars 25 20:10:52 gybbs gnome-session-binary[980]: GLib-GIO-CRITICAL: g_bus_get_sync: assertion 'error == NULL || *error == NULL' failed

Does anyone know how to fix these problems? And please explain them to me! ^^'

Thanks for your help (and sorry if the topic is in the wrong category)!

Welcome here, at LQ!

What you posted is not enough to help you. Would be nice to know more about the situation. Exactly what OS/version is it, what kind of hardware is it? Would be nice to know what did you [try to] configure.

Thanks for the welcome!

So, I'm running Ubuntu 22.04.4 LTS, using a fixed PC with a pretty good configuration, and as for what I've configured, the list is pretty long haha, but it's mostly focused on security and the suggestions/warnings from my system audit (done with Lynis). Thank you.

You are getting responses in ubuntu forums where you cross-posted: https://ubuntuforums.org/showthread.php?t=2496373 I found that by googling the errors. It is a useful thing to google an error and helpful too.

gets quite a few hits

Yes exactly, I posted my error on several different forums in order to get as many responses as possible.
It's true that it's silly but I didn't think of googling my mistakes right away, thank you very much for the tip lol!

I have a question: if I uninstall/reinstall Ubuntu to factory state, my problems will logically be solved. Because I've been doing a lot of testing, changing, uninstalling and reinstalling third-party services/packages in a lot of different ways, and I think that's what's been causing me all my problems (removing packages that are useful for the system to work properly, for example?). So I'd like some advice on the best way to do it (a clean install), and if there's any software/services I should install/configure for better security (iptables, ufw/firewalld, clamonacc/OnAccessScan, fail2ban, rkhunter/chkrootkit, timeshift...)? Thank you very much for your help.

In such cases hard to say anything. I you want to do it just do it. You can create a clean install and save that main partition, next time you will be able to restore it in minutes. Otherwise just run the official installer.

Welcome to LQ

As several other community members have mentioned, it would do everyone in the picture if you could provide us with more information; you may potentially be able to find leads that may help us solve your problem, which can be found in the /var/logs directory.

Re. I installed Liux Mint Cinnamon, the installation went well, everything works great, I made my configuration as I wished, thank you all for your help.
I no longer have any errors or problems (with my sound, for example, which was constantly crackling under Ubuntu). Thanks a lot!

in that case you might want to mark the thread solved

Your initial post shows several errors relating to 'gnome-session'. Couldn't tell you what that's about but I would suggest that if you are making configuration changes to your system, you keep a record of the changes, how you made them and a link to any site or source you used to make the changes. Much easier to get help if you have details.