First, turn on the VPN, select global or smart mode, and then open Fiddler. If Chrome has SwitchyOmega installed, choose the system proxy.
If you need to control whether Chrome web pages go through Fiddler for packet capturing at any time using SwitchyOmega (only for domestic websites, as choosing other proxies will not allow packet capturing), you can create a new scenario mode in SwitchyOmega.