I'm basically in the same situation as Zoleta, except for one thing: I played on Link for years before havinig this problem. Without changing anything in my configuration I can't find any game anymore for some reason.
Port test always failed (tried with manual config, upnp and even dmz) but I was able to play anyway so no big deal, until 2 years ago. Now I can't find any game even where I know I have all the DLC and the same TU as others.
Also I used to play without problem with a friend that lives only 5 miles from me and now it doesn't work anymore even between us so it can't be a ping/speed problem.
All this to say: sometimes it's not your fault, you have only a shitty ISP 😪