Can an iMac 18.3 be upgraded to macOS Sonoma?

Hello. I have an iMac 18.3 that's only 5 years old, and I can't understand why it's receiving such limited support. It's the Mac with the shortest support lifespan in history. Furthermore, it can't even be used as an external monitor for another device. And all this while Apple claims to be an environmentally conscious company! Or is it only concerned about its bottom line? Is there no possibility of upgrading to macOS Sonoma? Will it at least receive security patches?