Install Debian stable 12 bookworm on the PC, with Gnome Shell destkop environment.
We need to install gnome-kiosk package. gnome-kiosk is not available on Debian 12, but it will be in the next version. In the meanwhile, you can follow the guide here to convert your Debian 12 into a Debian unstable (sid).
After installation, upgrade and reboot, as root install the gnome-kiosk package:
apt install gnome-kiosk
Optional: install ssh server:
apt install openssh-server
Edit the /etc/gdm3/daemon.conf file.
In /etc/gdm3/daemon.conf, and uncomment both AutomaticLoginEnable and AutomaticLogin lines. Put the username you created during installation in the AutomaticLogin line. Save the file and exit the editor.
Reboot. You will be automatically logged in. Logoff.
On the main login screen click on the user name, a gear icon will appear on the bottom right. Click on that icon and select Kiosk Script Session (Wayland Display Server). Enter the user password and login.
An editor will appear, il will allow you to edit the ~/.local/bin/gnome-kiosk-script file. Remove or comment the line starting with "gedit". Add a line to start firefox in kiosk mode with your favorite URL:
firefox --kiosk https://www.debian.org
save the file and exit the editor.