In your logs of apache appears:
[Wed Sep 02 08:54:48.432165 2020] [proxy:error] [pid 58635] (61)Connection refused: AH00957: HTTP: attempt to connect to 127.0.0.1:3000 (127.0.0.1) failed
In the guide, you configure apache with 3000, who is the default port for the Express server.
In this case, you had customized your application to use a different port, so you need to change to the apache configuration to use 3007.
In short, what you need to change is:
ProxyPass / http://127.0.0.1:3000/
ProxyPassReverse / http://127.0.0.1:3000/
ProxyPass / http://127.0.0.1:3007/
ProxyPassReverse / http://127.0.0.1:3007/