Also common to see in printed probability/impact matrix
However, HTML or excel(AFAIK) doesn't allow this visualization, so previous style is not common to see in digital content.
I think the more standard/common options are:
Fig1 has be the format/style more compatible with CSV (just missing color and bold)
Are there other options? Is there any theory or study about this type of tables? What do you think is the best solution in terms of UX?
Is there any modern language or technology that supports the cell with 2 values separated by a diagonal bar?