Revert VKS to 3.4.1. This will require the deletion and re-creation of the supervisor using VKS 3.4.1. Side effects will be that existing DSM clusters will be deleted, and the vSAN File Services fixes that are in 3.5 will be reverted as well.
Wait for DSM 9.0.2 to be released that corrects the VKS API incompatibility issue, and in parallel stick to DSM Classic for existing testing.
Make no changes to the existing supervisor and environment, and build another environment for DSM with VKS 3.4.1.