Update: I got Intel iGPU HW decoding to work. I really do think this has to do with file/folder with permissions when installing from HexOS UI.
I installed Plex (plex pass image) from the TrueNas Scale UI
Setup the User ID and Group ID to 569 (becasue my original Plex install was using 568)
Web Port 32401 (again becasue original Plex install was using 32400)
Checked off "Host Network"
Set up the Data, and Cofiguration Storage locations all as ixVolume (Dataset created automatically by the system)
Setup Logs and Transcode Storage as Temporary (Temporary directory created on the disk)
Add additional storage locations. In my case I only use Plex for Movies and TV shows so if you need Pictures, Videos, etc.. add those as well
Type (Host path that already exists on the system)
Mount Path /Movies
Host Path /mnt/HDDs/Movies
The make one for Shows
Type (Host path that already exists on the system)
Mount Path /Shows
Host Path /mnt/HDDs/Shows
select your options for CPU and Memody dont forget to check Passthrough available for (non Nvidia GPUs)
Next we need to make a new User and Group in True NAS so navigate to Credentials then Users
Name it whatever you want "Plex 2" in my case
disable password
UID 569
Uncheck Create New Primary Group
Primary group select apps
home directory
/mnt/HDDs/Aplications
I clicked ALL the permissions for Read Write and Execute
Unclick SMB User
Save
Now we need to create a Group
In TrueNAS navigate to Credentials then Groups
GID 569
Add Local Administrator to the Privelages selection
The Last thing we need to do is give our user and group 569 access to the SMB shares on TrueNAS
Navigate to Datasets in TrueNAS then Movies
click edit on the permissions button
Now add Item
Who is set to User
User is set to whatever you named your User in the previous step. In my case it is "Plex2" it shoud be in the drop down list.
under permissions select Full Control
Click Apply permissions Recursively and confisr the selection then continue.
Now add another item
Who is set to Group
Group is set to whatever you named your Group in the previous step. In my case it is "Plex2" it shoud be in the drop down list.
under permissions select Full Control
Click Apply permissions Recursively and confisr the selection then continue.
Now click Save Access Control List.
You should now be able to launch your Plex app and go toyour transcode settings, select your iGPU and transcode hapily ever after!!
If this doesnt wor for you i would also try changing the permissions in the aplications forlder for your plex user. it is my understanding that inorder to transcode plex needs to be able to execute commands and unpack folders it downloads inorder to be able to HW transcode. but im not 100% sure.