No certification needed, you just need to get the ITIL MALC Certification, read my topic ITIL Managing Across The Lifecycle Certification. Since 2019, this certification is not available for ITIL 4, only if you are coursing the ITIL V3.
From this level, you will have the right to become the Jedi of the ITIL, by trying to be ITIL Master, in this case, read my topic ITIL 4 Master Certification.
The ITIL Expert is only available for the ITIL V3 so if you are coursing for the ITIL 4, this certification doesn’t exist so you will have to take the ITIL 4 Managing Professional, so why get certified ? For that, check my other topic ITIL 4, the new ITIL for 2019.