How to schedule your computer to shut down automatically?

As the topic. With the help of which program you can perform the function of automatic shutdown of the system every day at the set time.

With a cronjob or by creating and enabling a systemd timer:

https://unix.stackexchange.com/questions/438741/use-systemd-shutdownd-schedule

When login is performed issue as root:
shutdown 17:30

Since you tagged Gnome, and probably you want a sort of UI like options, to avoid Terminal commands, you can make use of this extension Shutdown Timer - GNOME Shell Extensions

Is it possible to set a schedule in it because it is important to me.

Using systemd-timers:

Create the service file:

sudo systemctl edit --force --full scheduled-shutdown.service 

and add the following content:

# /etc/systemd/system/scheduled-shutdown.service
[Unit]
Description=Shutdown the computer

[Service]
Type=oneshot
ExecStart=/usr/bin/systemctl poweroff

Then, create the timer file:

sudo systemctl edit --force --full scheduled-shutdown.timer 

and add the following content:

# /etc/systemd/system/scheduled-shutdown.timer
[Unit]
Description=Shutdown the computer on the given time

[Timer]
# Shutdown on 18:00 on every day
OnCalendar=*-*-* 18:00:00

[Install]
WantedBy=timers.target

Then you can enable the timer with:

sudo systemctl enable --now scheduled-shutdown.timer