Liquid Threads namespaces are for discussions and aren't notable, so shouldn't appear in Special:UnconnectedPages.
e.g.
Thread namespace: https://www.mediawiki.org/wiki/Special:UnconnectedPages?namespace=90, https://en.wikinews.org/wiki/Special:UnconnectedPages?namespace=90
Summary namespace: https://www.mediawiki.org/wiki/Special:UnconnectedPages?namespace=92, https://en.wikinews.org/wiki/Special:UnconnectedPages?namespace=92
Comments namespace: https://en.wikinews.org/wiki/Special:UnconnectedPages?namespace=102
There's also a similar namespace on dewikinews that should be excluded, but I'm not sure if it's using Liquid Threads or not: https://de.wikinews.org/w/index.php?title=Spezial:Nicht_verbundene_Seiten&namespace=102
See also:
T113444: [Task] Exclude Page namespace from Special:UnconnectedPages