Hi,
Hovertemplate should be a template string with some special syntax, which allows you to combine x and y coordinates easily with the text. That said, I don’t think the pre-defined variables would contain both the percentage and count in your histogram, therefore you need to specify the two columns as customdata.
Here’s a recent thread about this very same topic: Histogram plot hover data not showing all columns - #2 by jlfsjunior
Hope this helps!