There is a Swingman camera though, but it's less practical to properly select the waypoints, though I can sort of manage. I'm trying to smooth out the beginning and ending of the fastest path to make it a single line. As it is now, the AI breaks and makes a fictive chicane before going back on its way
A few possibilities Your supposed to be able to highlight the number of waypoints crossing the finish line and simply select smooth. Sometimes you cant fine tune waypoints until you select find corridors. I have run into that when making pit paths. In the path screen you can select the path that allows edit. Maybe your path is selected in viewing rather than edit.
Have you read the old docs on this process? Almost sounds like you're editing individual points by hand - it was stated very recently that a lot of smoothing (as mentioned above) is done all around the track to avoid AI slowdowns. The start/finish join is addressed specifically in the AIW guide. https://www.studio-397.com/modding-resources/
There is a three part video series in addition to the guide link @Lazza provided Creating a new AIW in rFactor 2 - Part 1 Setup and Loading a Track in Dev Mode - YouTube
I didn't see this one ! Thank you, I was only using the other and some parts are a bit blurry to my mind. It should be easier with this one, thanks a lot