Well, found a way around this for PC (not PS4/Xbox)
First install/activate JSMXE. Rob a copy from Assetto Corsa root folder if you need to or google it.
Download the PC2 boot file...
==== Addon Car Downloads ==== For Project Cars 2
projectcarsmoddingteam.weebly.com
from the link and within the boot files (mod folder) go to vehicles folder and to the "vehicle list" at the bottom in the vehicles folder - open and cut the crd at the end of any car you want to hide in that "vehicle list". Then use JSMXE to re-activate the boot files and voila any cars you want - vanished!
I would like to thank my mom, my pop, my great great great gran for helping me overcome this life long challenge.
And btw - I think many people are missing a trick with PC2 as the latest POP FFB files do some magic to PC2 and dare I say it, it drives and races better than my beloved Assetto. All the important tracks in HD glory and modern looking, all the cars and all the apps built in and work and look good. In addition there are around 120 mod cars. But honestly, I think PC2 was a bit of a mess when it came out and the pitchforks were never put away and yes the FFB was lifeless but not anymore. IMO it's madness to ignore PC2 for AMS2 when PC2 offers so much more now and in a steam sale you can buy it for £7 quid and the whole entire season pass for £11.
Gave AMS2 a chance and bought into it but man going back to PC2 has made me realize I already had something really good - just needed to change the FFB file to the latest modern ones.
*I don't work for SMS