見えたみえた(ルータでWANのUPnP有効)
$ sudo nmap -Pn -sU -p 1900 --script=upnp-info
Starting Nmap 6.40 ( http://nmap.org ) at 2021-06-28 08:10 JST
Host is up.
PORT STATE SERVICE
1900/udp open|filtered upnp
Nmap done: 1 IP address (1 host up) scanned in 14.06 seconds
nmap.orgNmap: the Network Mapper - Free Security ScannerNmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
無効にしたのわよ 
PORT STATE SERVICE
1900/udp open|filtered upnp