AV1 encoder initialization fails with status code 8

I would like to use the AV1 encoder of the video codec SDK but am having trouble to correctly instantiate it. At first I thought this was a problem with my implementation, but I can reproduce this with the AppEnc* application in the Samples suite of the video codec SDK 12.2.

To do so, build the sample suite, and run, for example, AppEncD3D12.exe [-i ...] [-s ...] -codec av1 and you will get: NvEncoder::CreateEncoder : m_nvenc.nvEncInitializeEncoder(m_hEncoder, &m_initializeParams) returned error 8. What is the cause here?

While debugging, I followed the instructions to set up the NV_ENC_INITIALIZE_PARAMS structure with the most basic settings (and set the encodeConfig member to NULL as recommended in the documentation to use the default settings) with the same result: error 8. I have been unable to initialize any AV1 encoder so far.

H264 and HEVC work without any problems. Hardware is an RTX 4500, SDK version 12.2 on Windows.