I don't think you can set a specific Logitech profile for Forza because it is UWP. So, in the Logitech Global Device Settings, I have:
100%
100%
100%
Check center spring, 0%
Uncheck Combined
260° (It seems the game forces all steering wheels to 180° rotation limit. Even then, the in-game steering will be somewhat less than whatever you set here. Setting it at 260° seems to be the smallest value that will allow the game to go its full 180°. The motor-lock of the G27 happens a little beyond where the game stops turning, though. Avoid the cockpit view that shows the drivers hands for less weirdness.)
Check allow game to adjust
In game, I have:
Vibration: 30
FFB: 100
Sensitivity: 100
Linearity: 50
Understeer: 170
Min Force: 100
Damper: 5
Center: 5
You could start with these settings and see what you think, then tweak things from there.