Data modeling help for a newbie

For doing this type of grouping I've found it much easier to build a separate Excel file that lists all training titles in one column and then add the group name for each training in a column next to it. Then you can import the Excel file into Power BI and do a merge of the Excel file into your main table. Then you can use that column in any visual without needing to write any code.

I'm not in front of Power BI at the moment so I don't want to comment about the other things and lead you down the wrong path if I've got some incorrect things.

Also, the Matrix visual is Pivot Tables for Power BI.