So in the end, after trying multiple approaches, I ended up with intercepting button presses after switching layers in a gig script, which switches internal banks and notifies all other scripts. One extra button press to confirm and update LEDs. Not perfect, but this is what I liked best after all.
And I pretty much completed the whole thing, with full LED sync for X-Touch Mini, even using different LED modes there, so things now blink, knob LEDs switch to different modes indicating various states and availability of widgets for various parameters, so I now can adjust everything without looking at the screen, finally!!!
Here’s the updated gig file with everything
Also made an overlay template
And the whole thing grew to some 1.5K lines of code, because so unwieldy that I had to get a repo on Github to track everything, like a real grown-up developer almost! 