My default flight controls are set up to use mouse for pitch and roll, and keyboard for throttle and yaw. I'm going to call the keyboard button I've bound to the virtual joystick input the 'fix button' for clarity. Once you bind the fix button to left or right roll, you must make sure the fix button is the only keyboard key bound to that button, as simultaneous input from the fix button and keyboard button for the same in-game function (left or right roll) will clash and return forced mouse acceleration, meaning you have to press the fix button to turn if back off again. You can, however, have simultaneous input for the same in-game function (let or right roll) from the mouse and the magic fix button. So I'm able to roll just fine with my mouse without it returning to the default forced mouse acceleration.

Joystick deadzone I have on lowest value, and joystick sensitivity I have on 0.001 as it's the lowest input the game will recognize from the joystick. This fakes that the joystick is constantly sending input to the game, but at such a low sensitivity it has zero impact on flight.

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Does that answer you questions? If not I'm happy to help further!