Any armature with a skinned mesh — UE5, Mixamo, Rigify deform bones, glTF characters, quadrupeds — and skeletons with no mesh (BVH motion capture). Bone names do not matter.

Yes. The treadmill speed of an in-place clip is found and taken away before deciding which foot stands.

In Unity 6, on six sets of animation, every event landed in its clip at the right time, and at 79% of the footsteps and landings the foot had just come down onto the floor in the engine (with the same events shifted in time: 12%).

No. It replaces only its own OnFootstep and OnLanding events and its own StepSync curves.

Yes: add an Animator float parameter named like the curve (StepSyncLeft) and read it as an IK weight.

Unity in this version; the steps file is plain JSON for any engine.

No.