The unique values in two or more fields are categorized as 'all other values' in ArcGIS Online.

Workaround

For the counting and categorization, create the following expression in ArcGIS Online:

This displays the categorization as it is in ArcGIS Pro, but without the labels.

Note: Whenever the name of each category is changed, the value of the first field of the relevant records is changed.

Steps to Reproduce