Exported h264_nvenc and hevc_nvenc video when played with Windows codecs (WMP, Movies...) shows a video that is just a little bit late behind sound (desynced), I could say even that it is hard to notice but it is visible. Same video works perfect with VLC or K-Lite Codec Pack or when imported in any other video editor just with Windows h264 and with hevc video extension plays desynced as I explained. On the other hand video editor Shotcut render hevc_nvenc that plays normaly with Windows codecs and video players and it is based on MLT and ffmpeg just as Kdenlive so I guess that Kdenlive developers could fix this so that exported hevc_nvenc and h264_nvenc plays normaly (synced) with Windows mp4 codec and HEVC video extension trough WMP or Movies. I tried to change audio codecs and bitrate and almost all settings available but I could not make it work just noticed that video is a little closer to sound when I m using just libx264 or libx265 without nvenc acceleration but it is much slower rendering. I need just hevc_nvenc to export video in sync with Microsoft HEVC video extension just for better compatibility with others, it would not be a problem for me becose I can always use VLC or some other player and open source codecs to watch it. h264_nvenc is not a problem becose I use it just for sending to Youtube and it's servers render normaly sent video exported with h264_nvenc and Kdenlive
I found a solution, it was easy, it is important to enter beside other wanted sethings this 3: Buffer size = 1500KiB; GOP=125 frames and Bframes=0 Then exported hevc and h264 file is playing exactly synced audio/video with Microsoft HEVC video extension and Windows native mp4 codec. (The problem was visible mainly when you are watching when someone is speaking, of course) It’s not even a bug, just settings tweak. Hope this helps someone. Bye