Unable to enable remote access

Did you already have a look at the related troubleshooting support article?

https://support.plex.tv/articles/200931138-troubleshooting-remote-access/

There’s also a guide with some more details on how to troubleshoot remote access issues. If that doesn’t help fixing your problems you could share the specific findings (e.g. if you can access/see the defined public/external port from your port forward on the router from outside your home network).