[V7] I'd like to sort it in the first header line, is there any way?

[2jordan3]

I'd like to sort it in the first row, is there any way?

The header is being merged and used.
This part is a way to cover the second line using rowspan and show the first line by hanging down.
However, in this case, it is impossible to sort in the first line.
Is there any way?