I'm using APEX 19.2.
It seems if Interactive Grid column type is plugin, even source column data type is number, you can't use aggregation e.g. sum on that column. In aggregation only count is available.
I did create example on apex.oracle.com, where “Sal” and “Comm” columns type is plugin. If you try add aggregation on those columns only count is available.
In my example I have used plugin from below link, but also tried create my own plugin and explore all possible options without finding how get all aggregations that out of box column types gives on number column.
Is there anyway get other aggregations e,g. sum, and average work if column type is plugin?