I edited the default VRChat locomotion animation layer to both disable the walking animation when I'm crouched and also allow it to be toggled off when I'm at normal height.

A download link: https://mega.nz/file/mlJlxI7I#MolgiLCJeUZq3P7bldZc5RmdGXMAfIs2u-jS2Zywi2g

How to use:
1. Disable the "Force Locomotion animations for 6 point tracking" option.
2. Set your base animation layer to the provided controller.
3. Optionally: Use the provided expression menu and parameters files, or add the parameter to your existing one.

One minor issue exists: there is a small delay between you stopping movement and the animation ending. This is because the VelocityX and VelocityZ parameters are smoothed and do not actually reach 0 the moment you stop. You can observe this delay by using the debug menu.