Which OS version runs on my rapsberry?

Currently the latest version number of Raspberry Pi OS (aka Raspian) is 12 (Bookworm).

But which one is running on my Raspberry??

cat /etc/os-release

tells you!

PRETTY_NAME="Raspbian GNU/Linux 11 (bullseye)"
NAME="Raspbian GNU/Linux"
VERSION_ID="11"
VERSION="11 (bullseye)"
VERSION_CODENAME=bullseye
ID=raspbian
ID_LIKE=debian
HOME_URL="http://www.raspbian.org/"
SUPPORT_URL="http://www.raspbian.org/RaspbianForums"
BUG_REPORT_URL="http://www.raspbian.org/RaspbianBugs"

The different versions and their nicknames are
7 (Wheezy)
8 (Jessie)
9 (Stretch)
10 (Buster)
11 (Bullseye)
12 (Bookworm)

Which hardware version ?

cat /sys/firmware/devicetree/base/model

see also https://www.elektronik-kompendium.de/sites/raspberry-pi/2006071.htm