Yes, Spine skeletons are rendered as dynamic meshes by SkeletonRenderer.
Just to point how they are currently being destroyed:
You'll find the OnDestroy of SkeletonRenderer calls rendererBuffers.Dispose();
spine-runtimes/SkeletonRenderer.cs at 3.6
Which disposes the smart mesh class:
spine-runtimes/SpineMesh.cs at 3.6
Which ultimately calls UnityEngine.Object.Destroy(mesh) on the meshes.
spine-runtimes/SpineMesh.cs at 3.6
I'm not sure if Unity's Switch support may have some different behavior regarding this.
If you can iterate quickly, it may be worth checking the hideflags of the dynamic mesh generated:
spine-runtimes/SpineMesh.cs at 3.6
Also, currently, SkeletonRenderer's MeshRendererBuffers rendererBuffers
is a private member so you'll have to modify SkeletonRenderer to do some things to it, either within it or from another class.
We've also had some user report mesh leaks a few months ago which we fixed. I hope you have a more recent version of Spine-Unity where those have been fixed.