Try and add output for the vonMises stress in the simulation domain. Take a look at the /Physics/SolidMechanics/QuasiStatic/QuasiStaticSolidMechanicsPhysics/generate_output parameter...

generate_output is a convenient way to obtain scalar quantities, such as tensor components, invariants, etc. as fields that can be visualized on a mesh.

Change your quasi-static physics block to

[Physics/SolidMechanics/QuasiStatic]
  [all]
    add_variables = true
    generate_output = 'vonmises_stress'
  []
[]

Then rerun the input and visualize the output. You will notice that the resulting field looks blocky. MOOSE is projecting the material point values onto constant monomial functions. The /Physics/SolidMechanics/QuasiStatic/QuasiStaticSolidMechanicsPhysics/material_output_family and /Physics/SolidMechanics/QuasiStatic/QuasiStaticSolidMechanicsPhysics/material_output_order parameters allow to select higher order monomials and even nodal variables for smooth material property output. For now let's just try a second order monomial with

[Physics/SolidMechanics/QuasiStatic]
  [all]
    add_variables = true
    generate_output = 'vonmises_stress'
    material_output_order = SECOND
  []
[]

If you load the result into paraview you will notice that for higher order monomials paraview automatically averages the results at the nodes. Nodal patch recovery is available to perform such a projection more accurately inside MOOSE.