Hey. I bought a GTX 1660 Ti a few months ago and I've also been experiencing micro stutters when streaming/recording using nvenc. After reading forums and searching for days or even weeks, I decided to give up. I even tried Nvidia Share (GeForce Experience), but it had the same stuttering.
But today, just testing out of curiosity, I think I found the possible cause and its solution: frametime variance seems to be the cause, and the solution is RTSS (RivaTuner Statistics Server) FPS cap.
I've only tested recording League of Legends, but it worked for me, fixing all the micro stutter. It seems nvenc is extremely sensible to frametime variance when recording, so anything different than a perfectly stable frametime will cause stutter in your recording. You can check this by enabling RTSS's frametime history overlay and comparing in-game FPS cap with RTSS's one. In my case, LoL's built in FPS cap had a very slight frametime variance (unnoticeable for human eye, but present in the graph), and RTSS's cap showed a perfect straight line all the time. So I had to test recording with RTSS FPS cap enabled, and voila!
tl;dr: just cap your FPS to 60 or 120 (maybe 180/240 works too?) using RTSS, and disable in-game FPS cap.
My setup has a 144 Hz FreeSync monitor + Nvidia Control Panel vsync (only works <144 FPS, you can read
blurbusters website to know more about this), but I guess it works the same without variable refresh rate.
Let me know if it helps.
EDIT: strangely enough, at least for LoL, I think you actually need to enable both in-game FPS cap and RTSS's. I only managed to record stutter-free videos with
both cap methods on. I had success with a 60 FPS cap and 120 FPS. My OBS (version 24.0.1) was set to record video at 60 FPS.