H.265 transcode requires a Kaby Lake or better. Personally, I rip 1:1 to an MKV, no changes to encoding. The Roku Ultra can stream H.265 directly, not sure about others, test your player.
For your use case, provided you are comfortable with a bit of a learning curve, I am recommending the Coffee Lake G5400 on x11sch-f (1). You'd use
@danb35 's script to create your Plex jail, so you are ready to enable hardware transcode when TrueNAS 12.0 rolls around. The learning curve is to become comfortable with CLI to a degree, and know how to create datasets and mount them into a jail, which requires an understanding of what a "file path" is. We have written guides, and videos as well, to help someone understand that process - and, fair enough, we've had users on these forums who struggle for a week with a task that should take 5 minutes, because the concept of a "file path" is just utterly foreign.
How steep that learning curve will be for you depends on your comfort level. You can gauge that by looking at this video, only the first 14 minutes, the rest isn't relevant to you:
https://www.youtube.com/watch?v=GvM32lWc_r4
If that has you running for the hills, then getting Plex with hardware transcode working is going to be bear.
If that has you going "yeah I can learn how to do that", you are in good shape.
(1) Specifically that board because it has C246 AND enables iGPU on the board / in BIOS