I am trying to increase the size of the 9x9 colour grid in the legend. I absolutely cannot find how to do it. There doesn't appear to be anything in the properties that will allow me to do it and increasing the size of the legend box by dragging the grips has no effect. Increasing the label text size has no effect (other than to increase the label text size). I've gone through every property I can find but nothing seems to do anything.
ArcPro 2.8 Desktop, Windows 10
If this is what you are referring to
Bivariate colors—ArcGIS Pro | Documentation
there is also no specific mention of changing the overall size.
Perhaps someone has posted something on Ideas as a feature request, if it truly doesn't exist
There isn't an automatic way to change the size, but you can convert to graphics and then resize the grid.