is extremelly popular in the US for chatting, much more than WhatsApp actually. However, there is no way to add this option.
As a business, I own a business iMessage account. I just need to allow my visitor to click on https://bcrw.apple.com/urn:biz:eaf88776-e7f4-41dd-86c1-3cbbca8b2ce7
As a result, you only need to add the option, the icon, and let me paste the URL.
Apple iMessage is native to macOS. So native that when you click on the URL above it opens macOS iMessage directly by default without showing any browser window.