In dolfinx, how to apply a fixed displacement condition to a vertex?

[dokken]

@French_fries

boundary_facets = mesh.locate_entities_boundary(domain, fdim, left)
u_D = np.array([0, 0], dtype = default_scalar_type)
bc = dirichletbc(u_D, fem.locate_dofs_topological(VU, fdim, boundary_facets), VU)

Replace fdim with 0.
i.e. instead of boundary facets, you want the boundary_vertices.