Meanwhile, can you please elaborate more on the issue you are facing? Is the proxy not being set when the Live Traffic toggle switch is turned ON, or are you facing trouble starting the application? Or is there possibly another issue?
Fiddler Everywhere requires administrative rights to set/unset the system proxy. Ensure your system covers all prerequisites listed in our documentation (macOS prerequisites here). If you can start Fiddler with administrative rights, and you have access to the login endpoints, but you are still facing the issue, then please send us the Fiddler Everywhere log files (accessible through Help > Open Application Logs Folder).
Alternatively, if you don't have administrative rights to set/unset the system proxy, you could try capturing traffic through the preconfigured browser instance option in Fiddler Everywhere.