why steam is using software encoder

[USS-Long Island]

i tried parsec and moonlight,they worked well with nvidia nvenc h264/h265.

but steam link keeps using libx264 to encode even if i turned on “use nvidia hardware encoder” in the advanced host settings.

streaming_log.txt:
"CaptureDescriptionID" "Desktop BitBlt RGB + libyuv + scale + libx264 main (4 threads)"
and in the taskmanager, cpu usage goes high but nvidia encode has 0% usage

i remember that just few months ago its was working well

i dont know why this happens

using a GP104 card which supports h264,h265 encoding