This is based in one comment made by Herbert123 in this Forum (*). Thank you for the idea.
To can edit sub-xSheets in its context is a big lost. You need it if you want to tackle projects with certain degree of complexity, mainly paperless type.

"To edit a sub-xsheet in its context:
Right-click the related xsheet icon on the right of the menu bar, and
choose Enable Edit in Place from the menu that opens."
(Toonz Harlequin User Guide pdf pag 217)
"2, We removed buttons for moving across sub-xsheet hierarchy in the menubar. Because this UI is rarely used in ink&paint or color design work, and also because it was, in our thought, not so much inportant function as occupying large space in the menu bar area. Instead of it, a text "(Sub)" is displayed in the title bar of Xsheet panel for showing whether you are in sub or parent xsheet. Moving accross sub-xsheet is available with the cammands in context menu of Xsheet."