Ok, so it sounds like you already know the answer here.
I tried Ch 6,7,8,9 and they all worked as the trigger source.
One caveat - they only worked with luxWrite. They would not work with virtualWrite.
I would really like “virtualWrite(ch, value, “digital_sensor”, “d”);” to work.
As an experiment I tried “virtualWrite(6, 1, “lum”, “lux”);” which I believe is equivalent to “luxWrite(6, 1);” And only the luxWrite worked as a trigger. Both widget appear identical. So there is something magic about the luxWrite. I haven’t tried the other write variants yet.
And it may be coincidental, but when I added a lot of widgets, the dashboard was very slow to respond. Almost unusable.