As far as I understood, in this specific case are exactly the same.
Differences between "Constraint Force" and "Total Force" of Weld Joint
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Which is the difference between Constraint Force and Total Force of Welded Joint in Simscape Multibody?
Constraint are defined as "Constraint forces/torque counter translation/rotation on the locked axes of the joint while allowing it on the free axes of its primitives." but in a welded joint there are no "free axes", since are all locked. In my opinion these two signals are basically equal.
Thank you and best regards, A