Consider adding a feature to modify the HOSTS file through the Fiddler Everywhere UI, similar to this feature in Fiddler Classic https://docs.telerik.com/fiddler/knowledge-base/hosts. 

Currently, there is no UI option to modify the operating system HOSTS file, so users must modify it manually as noted in the following documentation section: https://docs.telerik.com/fiddler-everywhere/capture-traffic/reverse-proxy#reverse-proxy-for-remote-web-servers.

Example:

Configure the hosts file on your OS to map www.example.com to 127.0.0.1.

On Windows:

# Add entry to hosts file (run as Administrator)
echo 127.0.0.1 www.example.com >> C:\Windows\System32\drivers\etc\hosts

# Verify the entry was added
type C:\Windows\System32\drivers\etc\hosts | findstr example.com

# Flush DNS cache to apply changes
ipconfig /flushdns

On macOS:

# Add entry to hosts file (requires sudo)
echo "127.0.0.1 www.example.com" | sudo tee -a /etc/hosts

# Verify the entry was added
grep example.com /etc/hosts

# Flush DNS cache to apply changes
sudo dscacheutil -flushcache
sudo killall -HUP mDNSResponder