You could do this with an Automation that has two steps. The first step would be a very simple
Run a script action using the following code:
const collaborators = base.activeCollaborators output.set("collaboratorEmails", collaborators.map(collaborator => collaborator.email))
The second step would be a
Send an email step that uses the output from the script as the value for the “to” field.
Running a script wouldn’t be a trigger. I suppose I should have asked: “When do you want to send a note to your collaborators?”
^ The answer to your question would be the trigger. If there is no schedule about it, and you only want to send it every now again with no relation to changes to data in your base, then its possible select any trigger and run the Automation manually.