Hi,
yesterday there was a new kernel 5.10.17 released by Raspberry OS devs. Maybe you can try it out
We had a similar report on this post, https://dietpi.com/forum/t/nfs-issues-blocky-choppy-playback-from-kodi-and-others/4959/6
There it was already find to downgrade kernel to 5.10.10
For the vc4-fkms-v3d this can be set using dietpi-config. However cma-256 would need to be added manually.