Historically the .NET/C# Driver has not supported the x509-related URI options because .NET didn't support PEM files out of the box and those URI options have been PEM files. .NET 5 introduced built-in support for PEM files:

https://www.scottbrady91.com/c-sharp/pem-loading-in-dotnet-core-and-dotnet

We should consider supporting the standard certificate-related URI options. Potential problems that must still be addressed:

1. As far as I know, .NET still doesn't have the ability to specify an alternate CA. Any CAs must be registered as a RootCA for the user or machine. We need to investigate whether this is still the case.
2. We currently do not have a net5.0 or net6.0 TFM in our production code, which would be required for working with PEM files. Not a big deal to add another TFM, but it would increase test times unless we drop an older TFM like netstandard2.0.