CLARIFICATION: I have to sheepishly confess that I mis-described that AEON button as having an “Open in Browser” floating Tool Tip designation. It actually says “Open Document” when you hover over it.
BTW, that is from the Inspector window, which is visible when one is creating a new Event’s details.
I neglected to add previously that if the Display preferences have been set to show the LINKS sub-section of Timeline Events, clicking on an email link there also fails exactly the same way described previously.
When I click on links from the Timeline itself I do get your contextual “Open in Hook?” window. Which works for all the apps I mentioned originally but again not for an Apple Mail hook. The contextual window does contain the correct text of all the kinds of apps links I have created so far. Only the Apple Mail ones don’t pass through. They always get that same error.
Putting tick marks in front of the hook link changes it in AEON. After entering the change the hook link now includes a prefix file://’ and a suffix '. I was unable to do anything further with that.
HOWEVER, if I leave the hook link alone BUT I enter the AEON Link’s editor mode from within the Inspector window and then highlight the entire hook link from there (there is no way to highlight the links directly in the Timeline itself) I CAN THEN USE THE LAUNCHBAR SENT TO FUNCTION. Command Key + holding Spacebar brings up Launchbar with the correct text of the link. I then simply hit Enter and voila: my email shows up error free.
So that seems to be the best workaround for now. 5 or 6 extra clicks or keyboard commands but it does give me back access to my hooked Emails.
Thanks for the suggestions and the extra info about how AEON works. BTW, they have a function they call SYNC by which they mean AEON links that open documents that have been saved into Scrivener and/or Ulysses. I have no experience with that but I may be playing with Ulysses later, thanks to its availability via my Setapp subscription.