Tested working for 1.16

PortMinerPlugin is a plugin version of PortMiner which lets you make your server public without manually port forwarding. It does this by using UPnP to open the port (usually 25565) on your router. Other applications you may have on your computer such as Skype, Bittorrent software and certain games already use this to open ports on your router. PortMiner automatically closes the port it opens when the server closes.
The plugin is new and may have some issues, so please report them on GitHub.

Non-Adfly Download Link

The plugin may have trouble finding your internal IP address if you've not specified it in server.properties and you have multiple interfaces (such as both Ethernet and Wireless connected, or VirtualBox installed, etc). To solve this you need to manually specify your internal IP in the server.properties.

To install, simply save the jarfile to your plugins folder.
The only command is /pmp, which tells you the version.

Please note, I do not accept responsibility for any damage this could cause to your router, computer, etc. Although this is highly unlikely, the plugin is relatively new and has not been tested on many routers.
Contains LGPL software from https://github.com/4thline/cling