Hello, I'm Going to Buy Pico-8, And I wanted to ask, Does Pico-8 run on a Raspberry Pi Zero W https://buyzero.de/collections/raspberry-pi-zero-kits/products/raspberry-pi-zero-w?variant=38399156114.
And if yes is there a way to make Pico-8 the "Operating System" so that it starts when I Booting up the Pc

Yes, PICO-8 runs on a Pi Zero W. Some of the more processor intensive games don't run at full speed (I like to use Dank Tomb to test), but it otherwise works. When you buy PICO-8, there will be a Raspberry Pi download option.

There are multiple forum threads on the topic of booting directly to PICO-8. Here's a starting point, with links to other threads: https://www.lexaloffle.com/bbs/?tid=29159