trigger that only runs when a certain field has changed, or when it has changed to a certain value

[apreboski]

I need the ability to run an action only when a certain field is changed and/or is equal to a certain value.

Use case: A request comes in.  Manager assigns a task to a subordinate.  When the assigned column is updated (trigger), an email goes out to requestor and assignee (action).

[egidiocs]

 yes, this is a must have functionality.

I think Microsoft "modern sharepoint" team is unaware of what is Sharepoint in its full functionality. Lots of functionality missing, you cannot even group a modern list by its ContentType.