This behavior is not safe, as dolfinx.fem.Function(..).vector does provide a view into data stored in the dolfinx.fem.Function(Vh). This data (and the underlying vector) is deleted when dl.fem.Functon(Vh) goes out of scope, which is right away. (This is due to PETSc’s modern garbage collection (https://github.com/FEniCS/dolfinx/blob/main/python/dolfinx/fem/function.py#L288-L290, garbage collection different between petsc4py 3.17.4 and 3.18.3 (#1309) · Issues · PETSc / petsc · GitLab).
Thus, if you want to use the petsc-vector generated by a dolfinx.fem.Function, you need to do it in two steps:
u = dl.fem.Function(Vh)
uvec = u.vector
If you just want a petsc-vector (not wrapped as a DOLFINx function), you can use:
dolfinx.la.create_petsc_vector(Vh.dofmap.index_map, Vh.dofmap.index_map_bs)