Hi @Jabulani Motloung,
Welcome to the Microsoft Forum for technical support.
Based on your description, I noticed that the version you are installing is Exchange Sever2016 CU12. To prepare schema for this version, you should use the command in the format:
Setup.EXE /m:upgrade /IAcceptExchangeServerLicenseTerms
For detailed information you can refer to this document: Setup fails for unattended installation of Exchange Server 2019 CU11 or 2016 CU22 or later - Microsoft Support
Please feel free to contact me if you have any queries.
Best,
Jake Zhang