Is there a way to trigger Outlook-Add-Ins (Web) from external? (Custom event activation)

Question

I am currently working on Office365 add-ins development and their communication via asp.net interfaces which are registered with entra id. I would like to open email templates from an external program. Templates can be created via ms-graph or by the outlook-add-in-api. But how can i trigger the outlook-client by an external process, for example a trusted api? I only found the event-based activation which, however, are not self
controllable events. Is there a way to implement a trigger without user-based-activity? Example: Tom is using a program for creating tickets. When he creates a ticket, a new email draft in outlook pops up with attachments, a sample text and most important recipients. He can change the mail manaully and send it. That is/was possible with the classic outlook for windows. However we would like to prepare for the new outlook update. In order to react to the new Outlook update, we have to adapt our programs.
We would like to avoid implementing all programs as new web applications, but would like to find a hybrid solution with web-apis for the time being. Thanks!