Did you get this to work Zakaria? Do you know if it also work for the helpdesk app?

You can do two field one for 'res.partner' and another one for 'hr.employee' and use attrs to make these field visible depending on Value on field A.

Another solution may be work , you can define field B as reference field

Thank you Mahmoud for your answer,

I have tried the first solution. I tried to hide a field defined inside a notebook page. However, the field is disabled and not hidden!

The second solution that you have suggested "fields.Reference" is exactly what I am looking for! However, I am struggling using it as I have not found much documentation about it. Is there a way to access from a function to one of the models defined in it and hide it?

Thank you again