I specify the HEVC codec with VideoGrabber.Encoder_SetStr(Enc_Video_Codec, “hevc”), but the video is recorded in H264.

Disable VideoGrabber.RecordingInNativeFormat.
By default, when VideoGrabber.RecordingInNativeFormat=true with URL sources, the video stream of the URL is not decompressed/recompressed, it is saved “as is” in the specified container (.mp4, .mkv, etc…), whatever the codec settings specified.