Hi @CADDMR
If you want to perform a structural simulation, firstly, you have to remove any interference in the model, otherwise, you will get the wrong results.

Regarding constraints, I am not sure this model needs such a number of the fixed constraints, especially on the inner face of the platform (where the force acts from above). Your model looks like it is too stiff.

Remember, your calculation model should behave as in real, so the constraints are a crucial part of preprocessing. I think you can use in some places frictionless constraints instead of fixed ones, allowing the movement.
You need to examine your design, how it works, and decide where to put certain constraints.
About constraints in Fusion 360 you can read here:
Structural constraintshttps://knowledge.autodesk.com/search-result/caas/CloudHelp/cloudhelp/ENU/Fusi...