In case of using Animation from Mixamo and combining Animation in Blender, export glb/gltf to Godot3.x (using helper)

Mixamo part

- Create Mesh only and Export to .obj or .fbx

- Upload model and set Rig points as Mixamo suggests

- Select desired animation and load Collada.dae file. Applying transform will be smooth.

Blender part

- Import downloaded file, then clear scale(Alt S) and Apply Transform(Ctrl A) of Armature (don't put this model in Godot, you have to Clear Scale and Apply Transform)

- Open NLA window, then Push down the desired animation

- Manage Material

- Select Mesh and Armature, then Export glb/gltf

Godot part

- Drag the file or Import and test it.