Using, server side
push "redirect-gateway def1"
push "dhcp-option DNS 8.8.8.8"
traffic does not travel to the new gateway (nor to the default gateway)
C:\>tracert
www.google.it
www.google.it [142.251.209.35]
1 * * * Richiesta scaduta.
2 * * * Richiesta scaduta.