No. You cannot instance something and have it weld/merge the vertices together at the same time - because such an operation would break the instances in the first place. If you only want to copy a mesh - without instancing - you can use Mirror Geometry. I doubt that it does weld the vertices though.
And yes, this is slightly annoying as you will get hard edges in the seams. But you can always edit the vertex normals of the instances.
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And yes, this is slightly annoying as you will get hard edges in the seams. But you can always edit the vertex normals of the instances.