After the initial startup, the Fiddler Everywhere application could only capture non-secure traffic (HTTP) while SSL traffic is not captured. To enable capturing and decrypting HTTPS traffic, you will need to explicitly install a root trust certificate via the HTTPS submenu in Settings.
Trust Root Certificate
The button installs and trusts the Fiddler root certificate (macOS and Windows only).
Capture HTTPS traffic
The option defines if Fiddler will capture HTTPS traffic or will skip it. It is inactive by default. To active it, the root certificate should be trusted first.
Export Root Certificate to Desktop and Trust Certificate
Expand Advanced Settings drop-down to show the Export Root Certificate to Desktop and Trust Certificate button. Click the button to export Fiddler the root certificate to the Desktop folder for manual import and trusting of the certificate.