Unfortunately, there currently isn't a direct way to disable DHCP option 121 on Windows client machines.
Here's how to mitigate the TunnelVision vulnerability (CVE-2020-1472) instead:
Patch Windows machines. Ensure all systems have the latest security updates, including the May 2020 patches for TunnelVision.
Segment your network. Isolate critical systems on separate VLANs or use NAC to restrict device communication.
Enforce strong network security. Implement practices like least privilege access, firewalls, and IDS/IPS.
Harden your DHCP server (if applicable). Restrict who can receive option 121 and limit the number of static routes provided.