I see there is a FR for the issue I face: Buttons in the centre of the Touch Bar
So maybe it is really not possible.
Mac natively offers buttons in the middle of the touchbar - such as confirmation calls (the blue "confirm" button when filling some form, for example)
Added a screenshot of that here:
Is it somehow possible to choose position:center for buttons in the touchbar with BTT?
I recall in some versions there was the option to center the button but that's gone, and it was never really working.
Currently the only way would be to add some empty space before the button (i.e. a black button without function). There is no built-in way to center as of now (centering doesn't fit very well into the left | scrollable | right paradigm I'm using for the BTT Touch Bar currently, but I'll think about it).
I see, however there is no way to detect prompts like the confirmation prompt when delete Trash contents, so there is also no way to show buttons centered only when those prompts are visible.
Will see if there is some way to detect if a prompt is shown, first...