the .net 4.* framework has very limited http/2 support. It's been on the roadmap for years, but no real progress. you might find some unsupported nuget libraries (interest seemed to drop once core has support).
the grpc library for 4.6 has limited support for http/2:
[https://learn.microsoft.com/en-us/aspnet/core/grpc/netstandard?view=aspnetcore-7.0
note: support for 4.* is really limited to bug fixes, not new features or protocols