i saw the the problem which some people had with there T300 Wheel. Topic was: "T300 DRIVES LIKE A PAD F1 2018 (PC)"
I have a similar issue and i already read about this in different forums. The problem is easy to explain. I have a thrustmaster TS-PC Base and the Ferrarie F1 Add-on wheel.
In the Thrustmaster-Profiler on a PC you can choose between two different Profiles, "Advanced Mode" and "Normal Mode". The differents are the amount of button you can use in each mode. 13 Buttons on normal and 23 on advanced.
Unforunalety if i put my wheel in to advanced mode, the game doesn't recognized it as a known controller. I still can set all the buttons and axes but as soon as i go on track i realized the wheel drives like a controller and not like a wheel. The problem is exactliy like in the topic i mentioned above.
And when you look in to the installationfolder under "..\F1 2018\actionmaps\" you can find the buttonmappings for some thrustmaster bases combiend with the f1 wheel in advanced mode.
So it should work. Can some confirm this issue?
The game offers so many buttons to map and with the only F1 Wheel from Thrustmaster you can only use 13 instead of 23 Buttons:(