microsoft oledb 12.0 is not registered

As you were saying that you have installed Microsoft Access Database Engine 2016 Redistributable, then the Microsoft OLE DB Provider for Microsoft Access should have been installed as well, since it is included in the redistributable package as far as I can remember.

However, if you are still receiving an error that the Microsoft OLE DB Provider is not registered or found, you may need to manually register the provider so follow the steps below: 

1. Open the command prompt as an administrator.

2. Navigate to the folder that contains the "ACEOLEDB.DLL" file. This file is typically located in the "Program Files\Common Files\Microsoft Shared\OFFICE16" folder.

3. Register the provider by typing the following command:

regsvr32 ACEOLEDB.DLL

Note: If you are running a 32-bit application on a 64-bit operating system, you will need to use the 32-bit version of regsvr32, located in the "SysWOW64" folder. In that case, the command would be:

C:\Windows\SysWOW64\regsvr32.exe "C:\Program Files (x86)\Common Files\Microsoft Shared\OFFICE16\ACEOLEDB.DLL"

4. Once the provider has been successfully registered, try running your application again.

If you continue to experience issues, you may need to reinstall Microsoft Access Database Engine 2016 Redistributable or repair your installation of Microsoft Office 2016. Try once these steps and let me know if that works for you.