Identify my Raspberry Pi board version

To identify the version of your Raspberry Pi, you can enter the command:

$ cat /proc/cpuinfo

The last three lines show the hardware type, the revision code, and the Pi's unique serial number.

Then browse Raspberry Pi DOCUMENTATION > HARDWARE > RASPBERRYPI > REVISION-CODES. You can search your hardware revision to find out the version of you board.

My board is Raspberry Pi 3 B+

Related:
~ How to check Raspberry Pi 4B reversion 1.2, it provide more option to check your board version.