I hit the same stuttering with 1080p x265 on a Pi 4 and it turned out to be software decoding; once hardware HEVC decode was actually enabled in Kodi it played 1080p smoothly, though 10 bit content was hit or miss. HDR10+ is the harder wall: Kodi on Linux basically drops the dynamic metadata and passes plain HDR10, so your Samsung just applies static tone mapping and you lose the peak brightness tricks. If most of your library is HDR10+ rips, a used Shield may still cost less than fighting this despite the price. Curious what your source files are, because remuxes that keep the HDR10 base layer look fine, it is only the dynamic metadata you lose.