Well, the story is somewhat like this, there is an AC League called AC-Friends who run WEC, GT3, GT4 amongst other categories in organized league events, you must have heard of it.
For a new person who has joined that league, he/she must qualify in a trainee category before getting access to the WEC or GT3 mods. The WEC and GT3 mods are made by
@Bonny and are private and only for the league members whereas the trainee category usually uses publicly available mods such as GT4 or old Lemans cars. This whole system was done so that people don't just join the discord group for the mods and then leave and also to develop a good AC league.
As a result of this, the GT3 cars and Lemans cars are very desirable for some, and although they are eventually released like the Mercedes AMG GT3, some people are just too desperate to get them. The RSR 2020 that you are making skins for was used in the WEC league of theirs and was leaked by one of the drivers, hence this version isn't as polished as the original mod author would like it to be for a public mod and is in fact a beta version of the mod that was never supposed to be released in its state.
The mod that you referenced in the video you posted is that same beta version that was leaked and was never supposed to be released. In fact, the video you referenced is just another AC YouTuber who wants to make content and is in no way related to Bonny or the AC Friends discord community. Its widespread use and distribution have given a sour taste to the original mod author who was originally planning to release the good one but is now having doubts.
Again no one can force you not to do this and I am not telling you anything, but it would be great if we respect the modders wish and not distribute it further.
Here are some photos of the final version which may be released one day if the original author feels like it.
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