COM interop error in XUnit test - 0x80040154 Class not registered when

I have an MSTest project (.NET Core 3.1) where I test a legacy COM assembly against a ported .NET Standard 2.0 assembly.

MSTest doesn't support Data-Driven Tests using CSV files (TestContext.Datarow) so I switched to Xunit Framework.

Xunit project also runs .NET Core 3.1 and I test exactly the same legacy COM assembly against the same ported .NET Standard 2.0 assembly.

However, I get the following runtime error for every XUnit test:

System.Runtime.InteropServices.COMException : Retrieving the COM class factory for component with CLSID {7BC4415F-756F-50E8-1DF8-5BC89D19B03D} failed due to the following error: 80040154 Class not registered (0x80040154 (REGDB_E_CLASSNOTREG)).

The COM assembly is registered and the GUID is correct. Can anyone help?