The marking above the hyphen there is an underscore — it’s telling you that hitting shift-hyphen will give you an underscore.

You may be using software that supports inserting an em-dash when you hit that combination, but I don’t believe that it’s the keyboard layout that dictates that.

searches

It sounds like Microsoft Word does something similar:

https://www.avantixlearning.ca/microsoft-word/how-to-insert-an-em-dash-or-en-dash-in-a-word-document-4-ways/

Use Ctrl with keyboard shortcuts to insert an em or en dash

To insert an em dash, click where you want to insert the em dash and then press Ctrl + Alt + – (minus sign on the numeric keypad).

To insert an en dash, click where you want to insert the en dash and then press Ctrl + – (minus sign on the numeric keypad).