When using Ubuntu, we may be disabled WIFI when we turn off VPN (such as ExpressVPN). The reason I write this post is to decrease your time to find the solution because I encountered this situation and took a long time with it.

When WIFI is disabled, we need to open Terminal and type like below:

nmcli network off

nmcli network on

The meaning of two command lines is to reset WIFI to off state and turn on. Yeah, hope this solution help you handle your problem.