The game Mechwarrior 5: Mercenaries doesn't correctly identify the device Thrustmaster T.Flight HOTAS X properly, and the in-game settings for HOTAS/joysticks is slightly lacking.
Instead you're asked to follow a PDF-instruction on how to configure your own mapping, but most of us don't want to redo this anytime we switch PCs and so I decided to store such a configuration for the HOTAS I own.
I found one pre-made by a user on reddit, but my specific settings may come to change over time, which is why I created this repo to keep track of the latest version.
The file needs to be stored in the folder %LOCALAPPDATA%\MW5Mercs\Saved\SavedHOTAS\ with the filename HOTASMappings.Remap
As always, save the original file in case you want to use the original file created by the game (in my case, the game threw out a config for THRUSTMASTER TWCS Throttle + THRUSTMASTER T.16000M Joystick).
The game doesn't support the Rudder/Slider on the T.Flight HOTAS X, so if you want to use it for turning the mech instead of the twisting axis (RZ) on the joystick, press the Home Button on the throttle to switch the device from 5 axis mode (green light) into 4 axis mode (red light).
Remember that you can physically lock the twisting (RZ) action of the joystick if you prefer using the 4 axis mode!