I have Cinnamon installed. When reboot or launch after shutdown I don’t have to type in a password. I would like to change that. I found an answer here, but that applies to lightdm.
How can I find out if I am running lightdm or sddm?
If I am running sddm, how do I stop auto-login?
There might be other ways to find it out as well, but the following two command lines should tell what display manager you are using:
systemctl status display-manager
or
grep 'ExecStart=' /etc/systemd/system/display-manager.service
If I remember correctly Cinnamon uses LightDM.
Your memory works pretty well 
: I am on lightdm.
Here is the output from the 1st command:
systemctl status display-manager
● lightdm.service - Light Display Manager
Loaded: loaded (/usr/lib/systemd/system/lightdm.service; enabled
and this is the output from the 2nd command:
grep 'ExecStart=' /etc/systemd/system/display-manager.service
ExecStart=/usr/bin/lightdm
Both refer to the/usr folder, although the 1st mentions subfolder lib, while the 2nd one mentions subfolder bin.
And in the article I linked to they mention /etc/lightdm/lightdm.conf.
Before raising this issue I had checked if /etc/lightdm/lightdm.conf was present on my system, as is autologin-user = <my username>.
So, can I then just comment out the line in the /etc folder?
And what about the /usr folder and its subfolders?
Yes.
You don’t need to touch anything there. /usr/bin/lightdm is just the binary that runs the display manager.
Have a look at the following for some info on Linux Filesystem Hierarchy:
https://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/index.html
Good info, thanks a lot. You provided the answer. Many thanks, once again. 
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