Hi giulia72
You can try with this trick
1) Duplicate your default layout and assign only the default for the home page
2) In your duplicated layout which you will assign to all other pages add the
<link rel="alternate" href="https://www.pcvuescada.com/" hreflang="en-gb" /> in to the Before </head> section of custom code tab
3) Apply the isolation as i suggested in THIS POST
Now you can choose to which menu items assign custom code simply assigning to it the choosed layout -
P.S.
You should remove the code from head.php file too
Hope it helps.