if you add thunderbolt.host_reset=false to the kernel command line then nvidia eGPU will works (i have tested this and confirmed this changes works with:
sudo midclt call system.advanced.update '{"kernel_extra_options": "thunderbolt.host_reset=false"}'
working (note a non-working system will show D3COLD errors in the output below, this is an issue on all recent LTS and mainline kernels on systems with USB4)
truenas_admin@HexOS[~]$ sudo dmesg | grep nvidia
[sudo] password for truenas_admin:
[ 36.563182] audit: type=1400 audit(1733276217.971:3): apparmor="STATUS" operation="profile_load" profile="unconfined" name="nvidia_modprobe" pid=2363 comm="apparmor_parser"
[ 36.563296] audit: type=1400 audit(1733276217.971:4): apparmor="STATUS" operation="profile_load" profile="unconfined" name="nvidia_modprobe//kmod" pid=2363 comm="apparmor_parser"
[ 114.962824] nvidia-nvlink: Nvlink Core is being initialized, major device number 235
[ 114.968129] nvidia 0000:39:00.0: vgaarb: VGA decodes changed: olddecodes=io+mem,decodes=none:owns=none
[ 115.122803] nvidia_uvm: module uses symbols nvUvmInterfaceDisableAccessCntr from proprietary module nvidia, inheriting taint.
[ 115.148763] nvidia-uvm: Loaded the UVM driver, major device number 511.
[ 115.156325] nvidia-modeset: Loading NVIDIA Kernel Mode Setting Driver for UNIX platforms 550.135 Wed Nov 13 23:35:58 UTC 2024
[ 115.161201] [drm] [nvidia-drm] [GPU ID 0x00003900] Loading driver
[ 115.161203] [drm] Initialized nvidia-drm 0.0.0 20160202 for 0000:39:00.0 on minor 1
[ 115.165157] [drm] [nvidia-drm] [GPU ID 0x00003900] Unloading driver
[ 115.224654] nvidia-modeset: Unloading
[ 115.273993] nvidia-uvm: Unloaded the UVM driver.
[ 115.331235] nvidia-nvlink: Unregistered Nvlink Core, major device number 235
[ 123.378230] nvidia-nvlink: Nvlink Core is being initialized, major device number 236
[ 123.384055] nvidia 0000:39:00.0: vgaarb: VGA decodes changed: olddecodes=none,decodes=none:owns=none
[ 123.507023] nvidia-modeset: Loading NVIDIA Kernel Mode Setting Driver for UNIX platforms 550.135 Wed Nov 13 23:35:58 UTC 2024
[ 123.509099] [drm] [nvidia-drm] [GPU ID 0x00003900] Loading driver
[ 123.509100] [drm] Initialized nvidia-drm 0.0.0 20160202 for 0000:39:00.0 on minor 1