The status showing as green and switching to red swiftly just means it’s not working. Plex optimistically lists the status as green while performing the status check.
Did you already have a look at this guide on how to troubleshoot Remote Access issues? The individual findings/output of the steps should give you pointers on where the issue is located — e.g.: can you see/access your manual port forward from outside your home network (using a service like canyouseeme.org) and does the public ip recognized there match that listed in the remote access settings of your server and the router’s WAN IP?
