Ok thank you, it works with libx264 
I see shotcut use libx265.dll to work.
I don’t know how to build it, i only know building a full ffmpeg.exe with all lib included.
The reason why 10bit for export is: not to have real 10bit, it’s because 8bit codec are all BAD to encode good 8bit color gradient (even AV1 codec) (however it’s good with very high bitrate). That makes sense for 8bit source and workflow.