Installed the last version of Elementary OS, updated. Setup in Users and accounts autologin (don't ask for password when system starts). Reboot the laptop, OS asks me for the password. Check settings and the checkbox is off for autologin. Turn it on. Reboot. Again asks for the password.

Any ideas?

sounds like you ran some kind of GUI (graphical panel) as non-root which is why IMHO it did not work

try opening a terminal and getting root then edit the file /etc/lightdm/lightdm.conf so that the line changes from
#autologin-user=<YOUR USERNAME>
to
autologin-user=<YOUR USERNAME>

ref
https://elementaryos.stackexchange.c...entary-os-loki

use arrow keys to get to # and delete it
then press kb keys Ctrl (and) o (to over-write file).....follow the prompts to agree to over write file-name
then press kb keys Ctrl (and) x (to exit nano)


2) if that scares you....run sudo <name of text editor> /etc/lightdm/lightdm.conf in a terminal to achieve same outcome.

Recently, on boot up or restart, my EOS system has been auto logging into one of the user accounts (the one I use most, call it user A) even though it is configured not to. I can log in with user B, then log out of user A, then log out of or restart from user B and get the greeter showing the users. Logging into user B requires a password, but selecting user A logs in user A without a password. Also renamed /etc/lightdm/lightdm.conf and edited io.elementary.greeter.conf as advised from a StackExchange EOS forum post, with no affect.
Any ideas on where to start looking to troubleshoot this issue?

Computer: Dell Inspiron 15-7568 laptop
OS: elementary OS 6.1 Jólni, latest updates
$: lightdm --show-config
[LightDM]
A logind-check-graphical=true
C backup-logs=false

[Seat:*]
A greeter-session=io.elementary.greeter
A user-session=pantheon
B allow-guest=false
D greeter-wrapper=/usr/lib/lightdm/lightdm-greeter-session
E guest-wrapper=/usr/lib/lightdm/lightdm-guest-session
F xserver-command=X -core
G autologin-user=

Sources:
A /usr/share/lightdm/lightdm.conf.d/40-io.elementary.greeter.conf
B /usr/share/lightdm/lightdm.conf.d/50-disable-guest.conf
C /usr/share/lightdm/lightdm.conf.d/50-disable-log-backup.conf
D /usr/share/lightdm/lightdm.conf.d/50-greeter-wrapper.conf
E /usr/share/lightdm/lightdm.conf.d/50-guest-wrapper.conf
F /usr/share/lightdm/lightdm.conf.d/50-xserver-command.conf
G /etc/lightdm/lightdm.conf