@Krakouille, you wrote:
So for now, I’ll continue to keep my many Mind Maps outside of Aeon Timeline. It’s a bit of a shame, because having them directly in Aeon would have been a real gain and would have avoided creating the same item twice (once in my external mind-mapping tool, and once again in Aeon).
If it’s down to how to manage a number of custom tabs, I get it. I have 14 right now, and likely will be adding more as needed.
I found a solution. I use a Stream Deck device, which sits next to my keyboard.
This is my default Aeon Timeline view, which automatically displays when Aeon Timeline is the active app. The highlighted buttons represent the custom tabs I most commonly view, plus an “All Tabs” option to show all available custom tabs:

If I select “All Tabs,” I get an expanded view of my available custom tabs, plus a few placeholder buttons to make it easy to add new custom tabs I create:

These buttons are quite easy to set up for the first nine shortcuts, because a button is assigned to the related keyboard shortcut. Easy peasy.
The challenge is that even though Aeon Timeline allows any number of custom tabs, it assigns keyboard shortcuts to the first nine:

But I have 14 custom tabs. How could I make Stream Deck buttons for the custom tabs that weren’t assigned keyboard shortcuts? I found a way, which I previously documented: How to extend shortcuts beyond the first nine custom tabs - Mac & Windows (Desktop) - Aeon Timeline
My solution, which uses AutoHotkey, works only in a Windows environment. As you’re on a Mac, I’m sure you could do something similar with Keyboard Maestro or other Mac-friendly automation tools. (AI is pretty good at helping with stuff like this.)
Anyway, I just wanted to suggest a path to help you achieve your goal of moving your other mindmaps into Aeon Timeline and still make it easy to see and select any custom tab.