"how could i do this with a 2-node environment and a "nested Wittness ESXi" ?" - a '2-node' vSAN cluster is comprised of 2 physical ESXi data-nodes + a 3rd Witness Appliance (generally ESXi running as a VM elsewhere), these are configured via:
Cluster > Configure > vSAN > Fault Domains > Configure Stretched cluster > Select and configure Witness.
Data in such a cluster is typically placed as data+data+witness placed across DataNode1+DataNode2+WitnessAppliance (e.g. 3 Fault-Domains).
Good documentation on 2-node clusters here:
https://core.vmware.com/resource/vsan-2-node-cluster-guide
" I read somewhere that i should have a option "nested Failure Domain" in the wizard for vm storage policy but i do not have them."
This is something entirely beyond regular FTT=1 in a 2-node cluster - this is additional per-node data protection, 2-node cluster option that requires minimum or 3 Disk-Groups per data-node: https://core.vmware.com/blog/nested-fault-domain-2-node-cluster-deployments