Create different grouped rows in a Matrix Visual

Yes, that's correct. You can't directly add the region grouping as rows below the matrix visual. However, you can use measures to calculate the overall sales for each region and then add those measures to the matrix visual as value fields. This will achieve a similar effect to having the region grouping as rows below the matrix.

Here's an example of how you can create a measure to calculate the overall sales for the North America region:

Sales in North America overall =
SUMMARIZE(
'Table',
'Table'[Sales Target],
"Region", "North America"
)

To create measures for the other regions, you can use a similar formula and just replace "North America" with the name of the desired region.

Sales in South America overall =
SUMMARIZE(
'Table',
'Table'[Sales Target],
"Region", "South America"
)

Sales in Europe overall =
SUMMARIZE(
'Table',
'Table'[Sales Target],
"Region", "Europe"
)

Sales in Asia overall =
SUMMARIZE(
'Table',
'Table'[Sales Target],
"Region", "Asia"
)

Then, you can add these measures to the matrix visual as value fields and they will show the overall sales for each region.

I hope this helps!