Hello In the old Launcher is possible to use the mod utility to create them and then use it with host server, but trying some days ago the new UI, I see that there are a lot of things that are better, but is not possible to use this applications. Do you plan in future to include it on the new UI?
The application exists in ..\Steam\steamapps\common\rFactor 2\Bin64 and is called "rFactor2 Dedicated.exe"
also you may should take a look here How to make a server with new UI | Studio-397 Forum (studio-397.com)
The right thing from my point of view would be for the new UI to have a couple of buttons for those applications. I don't understand why they haven't included them.
The problem is that I (and more users that I know) use Linux with SteamPlay/Proton to execute the game, and we can not execute the dedicated server using this instructions. Another option is to include this apps on the Steam Laucher as the graphical configuration