When Chrome Cannot Load a Local PAC File
Separate a rejected local PAC file URL from support for PAC routing, script syntax and the selected proxy.
If Chrome cannot use a PAC script supplied as a file:// URL, check that delivery path before rewriting the script. Failure to load one location does not establish that PAC routing is unsupported.
Chrome's proxy API has a pac_script mode, with script URL or inline data available through its supported extension interface. A local file supplied through operating-system settings is one particular way of trying to deliver the script.
Follow the script into the browser
Establish what controls the affected browser: system settings, managed policy, command-line configuration, or an extension. A value displayed in macOS settings does not prove Chrome obtained and evaluated that script.
Distinguish a rejected or unreachable script location from an evaluation error, and both from a failure to connect to the proxy returned by a valid script. The SOCKS port becomes relevant only after the browser has selected that route.
Distribute a managed PAC through an approved mechanism supported by the target clients. An HTTP or HTTPS delivery URL must remain reachable when the proxy it describes is unavailable. With extension-supplied inline data, changing the original file does not automatically update the copied script. For a small local policy at startup, embed the script in a data URL as another delivery path.
An internal PAC can contain private hostnames and routing rules. Keep it on an approved delivery service rather than moving it to arbitrary public hosting to solve a local-file problem.