You have a Plex Pass. You will be using hardware accelerated transcoding, which uses the GPU to transcode video (audio is always transcoded on the CPU).
The document you reference covers transcoding using the CPU, not the GPU. The information it contains regarding Passmark ratings does not apply to your situation.
To give you a reference point, I run Plex Media Server on a Synology DS918+, which as a Celeron J3455 CPU with Intel HD Graphics 500. Using just the CPU, the system struggles transcoding 1080p. Using the Intel HD Graphics 500 and hardware accelerated transcoding, it can transcode one 4K stream.
Your first post states you will have two users, one local and one remote. The i5-10400 with Intel graphics (not the F model) can easily handle that load.
If you want a Nvidia card then get one. However, given the workload you have described, it is not required.
Regarding transcoding 4K & HDR:
Just a reminder that transcoding HDR media is problematic in Plex.
Plex Media Server transcodes all media (not just HDR) to H.264, which does not support HDR. Furthermore, Plex Media Server does not map HDR colors to SDR colors (aka ātonemappingā).
As a result, many transcoded 4K HDR movies have a poor appearance, with washed out colors.
Where possible, you should plan so that you do not need to transcode HDR material. For example, this means not streaming 4K HDR movies to remote users unless they have 4K HDR equipment and both of you have the bandwidth to handle a 4K HDR stream.
Personally, I keep multiple copies of some movies - a 4K HDR version I use at home, and a 1080p SDR version I share with remote users. Using this approach I never transcode 4K media. It direct plays on my home TV. Remote users receive a 1080p version and do not have to worry about washed out colors.
This document has a lot of good, additional information regarding Plex and 4K media:
thank you for you informations.
I have another question, i5-10400 and i7-10700 have the same GPU IntelĀ® UHD 630.
If i use plex with hardware acceleration enable will i have the same performance?