Best way to encrypt some selected rows
Dynamic Data Masking (DDM) can fulfil the requirement as long as the Least Privilege Principle followed, since by default members of sysadmin server role and members of db_owner database role can always see UNMASKED (Including Encrypted columns).
If the requirement as such that even sysadmin role members must only see the encrypted data then the better fit will be Always Encrypted feature...
Or, if the goal is just to protect some sensitive data within database when it restored into DEV/UAT environments, better look for reliable third-party solution, or you can also develop you're own stored procedure/script that can be executed (manually) in DEV DB every time a restoration happened.