If your final setup is to host this ASP.NET Core web app on IIS, then please roll back all the changes you made in ConfigureKestrel
as they are not needed.
Instead, when you create the web site on IIS to map to your published artifacts, add an HTTPS binding to the site and select the desired server certificate.
Since you have the certificate and private key in the non-Windows native format, you need to use a tool like OpenSSL to combine them and save to a .PFX file. Then that .PFX can be imported in IIS Manager. You might read mypost for more details.