.NET Core 2.1 - How to create COM object and generate *.tlb file

This is now possible due to the work done on .NETCore version 3. As noted in my comment, hosting was the missing piece in earlier .NETCore versions with no substitute for mscoree.dll. Version 3 provides comhost.dll. Related, they also can now support C++/CLI code, ijwhost.dll is the substitute.

You register the component like you did with traditional COM servers, using Regsvr32.dll

Everything you need to know is available in this MSDN page, added a month ago. Do beware that .NETCore 3 is still preview quality right now. And this is Windows-only with no migration path for Linux and macOS, COM is too heavily tied to services that are only available on Windows.