I am very beginner, sorry, I would like for a pedagogical purpose to write a hook as in the example with an indication above … and I can not find the way …
thank you

Charly, for now, it requires a workaround.

Select the group of notes, and add a 1:1 tuplet (using the semicolon).

You can then hide the number, and manually add the letter using the text popover.

You may need to adjust the angle of the bracket in Engrave mode to make it flat.

thanks a lot Dan