For some unspecified reason, the data.difference function is not automatically prompted. Especially for you, I present how to use it :-). Since it is a "ghost" function you will not find it anywhere - neither on the function list nor in the Excel documentation, and you have to enter it completely yourself.
Function structure:
= date.difference ('start date', 'end date', 'type of calculation')
'start date' , 'end date' - here the matter is quite obvious so let me skip the description of the first two functions
'type of calculation' - with this third argument we can decide what difference we want to get expressed in years, months or maybe days?
An example of using the formula in practice: