WTelegramClient has no specific support for audio/video/group calls as it requires specific media streaming capabilities that are beyond the scope of this library.
You can of course call the APIs to establish a call, but then you would need to be able to stream voice/video to Telegram, otherwise it seems useless.
If someone wants to implement such a library (similar to https://github.com/MarshalX/tgcalls but for .NET, on top of WTelegramClient), it would be a welcomed effort.
Moreover, your question is about the advanced computation of end-to-end encryption keys as described here: https://corefork.telegram.org/api/end-to-end/voice-calls
WTelegramClient already supports a similar system for end-to-end encrypted messages (Secret Chats), but until someone plans to fully implement an audio/video call library (as I explained above) I don't plan to spend time on providing this kind of computation for end-to-end encrypted calls.