Av1_nvenc cannot use gbrp pixel format even if it should be able to

According to ffmpeg these are the supported pixel formats for av1_nvenc:

Supported pixel formats: yuv420p nv12 p010le yuv444p p016le yuv444p16le bgr0 bgra rgb0 rgba x2rgb10le x2bgr10le gbrp gbrp16le cuda

but if I try to use gbrp I get these errors:

[av1_nvenc @ 0x7f4760002c80] YUV444P not supported
[av1_nvenc @ 0x7f4760002c80] No capable devices found

hevc_nvenc and h264_nvenc both run fine with gbrp pixel format, only av1_nvenc has this issue.

My gpu is an rtx 5080-maxQ.