With the April 2022 update, for data privacy, social security numbers will be masked unless enabled in the users security profile.
To allow the full number to be visible the below must be enabled:
I recommend typing in the search field the word: "Mask" as this will bring up relevant settings. Check the box next to "Unmasked" and this will allow them to unmask the numbers.
On the HR Tab:
If the client has recruitment and collects Social security numbers from applicants, you may also want to enable them to view them unmasked as well. If you aren't sure you can allow unmasking.
Important: Unmasking is separate from the permissions field. I would only allow Unmasking when the respective field has permissions for view and/or edit.