If you're migrating from an on-premises proxy, you will already have a proxy setting configured...

When migrating from an on-premises proxy to Tunnel Mode, leaving legacy browser or system proxy settings in place can create loops or conflicting forwarding paths. Best practice is to enforce no proxy configuration so Client Connector owns traffic steering cleanly through the configured tunnel. Option B (Enforce no Proxy Configuration) is correct because Tunnel Mode should not depend on legacy proxy auto-configuration.

Why the other options are incorrect:

A. Execute a GPO update to retrieve the proxy settings from AD: A GPO can push Windows settings, but using it to reapply old proxy configuration works against Tunnel Mode best practice.

C. Use Web Proxy Auto Discovery (WPAD) to auto-configure the proxy: WPAD auto-discovers proxy settings; it can accidentally preserve legacy proxy behavior during a tunnel-mode migration.

D. Use an automatic configuration script (forwarding PAC file): A PAC file tells the client or browser which proxy path to use for matching destinations.