Why imac 2014 can not install macos Monterey?

Hello, dapeng17.

For various reasons, primarily hardware related, the 2014 iMac does not meet the requirements to run macOS Monterey.

macOS Monterey is compatible with these Macs - Apple Support

I'm sorry, my friend. There is no workaround but to buy a new or newer Mac.

It doesn't have the hardware to support it.

I can’t speak to this. I don’t know.