Avatar's Feet Not Touching the Ground" Error

Scenario 1: Capsule collider error

Select your Avatar node and select Edit Collider on the right. Then you can see the green capsule-shaped wireframe around the character.

Drag the dot on the wireframe to adjust the size of the capsule collider and make it entirely cover the Avatar.

Scenario 2: Long tail bone error

Select the tail bone and click the rotation icon on the toolbar to rotate the tail to a certain height.

Scenario 3: Animation issue

Adjust the animation as needed, for example, delete the displacement on the Y-axis.