Steps to reproduce:
When on a webpage, from the application menu bar select File>Share. The resulting share sheet should have a number of options. Messages is missing in Orion. It is visible in the share sheet for Safari and Firefox. I have tried compatibility mode. Messages is still missing.
Messages should be an option under the share sheet possibilities. (It is selected / enabled in System Preferences.)
Orion, OS version; hardware type:
Version 0.99.113.2-beta (WebKit 613.1.12)